Top PDF Terrestrial water storage changes over the Pearl River Basin from GRACE and connections with Pacific climate variability

Terrestrial water storage changes over the Pearl River Basin from GRACE and connections with Pacific climate variability

Terrestrial water storage changes over the Pearl River Basin from GRACE and connections with Pacific climate variability

The Pearl River is the third largest river in terms of drainage area and has the second largest streamflow in China. Due to its importance to the social-economic development of China, many studies [1 e9] have been conducted for water security concerns in the Pearl River Basin (PRB), e.g., rainfall regimes, drought and wetness, evapotranspiration, atmospheric water vapor, water discharge and sediment load. Among them, Zhang et al. [3] found that the PRB trends to be dryer in the rainy season and wetter in winter, and moisture content is one among many factors acting on the dry or wet conditions of the basin. Moreover, increased rainfall variability and frequencies of extremely high/low rainfall events related to the weakening Asian monsoon [4] as well as the frequencies of short wet periods with increased total amount of precipitation [1] potentially increase the risk of floods and droughts over the PRB. Furthermore, decreasing evapotranspiration result mainly from increasing aerosol and intensifying urbanization may weaken the hydrological cycle in the basin [2]. These studies have been valuable for the characterization of the PRB 's hydrological regime. However, recent strong anthropogenic influences, such as damming effects by the Longtan Reservoir (LTR), have significantly impacted the hydrological cycle of the PRB [8]. In addition, the upper and mid-PRB is formed primarily by a karst geological environment with strong heterogeneities [10,11], making it a great challenge to monitor and simulate water variations in these areas. Therefore, a combination of precipitation and other datasets (e.g., satellite observations and hydrological models) would be beneficial for a more comprehensive analysis.
Show more

9 Read more

Using GRACE in a streamflow recession to determine  drainable water storage in the Mississippi River basin

Using GRACE in a streamflow recession to determine drainable water storage in the Mississippi River basin

The relatively recent (e.g., 2000–current) availability of satellite-based Earth observations has generally improved our understanding of water stores and fluxes at varying scales, during normal and under extreme conditions (Als- dorf et al., 2010; Beighley et al., 2011; Swenson and Wahr, 2009; Kim et al., 2009; Reager et al., 2014; Sproles et al., 2015; Riegger and Tourian, 2014; Riegger, 2018; Tourian et al., 2018). For example, the Gravity Recovery and Climate Experiment (GRACE) satellites launched in 2002 provide monthly changes in total water storage resulting from water mass effect on the Earth’s gravity field (Tapley et al., 2004). These changes are computed as total terrestrial water stor- age anomalies (TWSA) and describe the monthly difference in storage state from the record-length mean. Due to of the ability of the satellite to measure changes in the entire verti- cal column, including surface and subsurface water storage, these first-of-their-kind measurements have provided a valu- able tool for understanding seasonal and interannual subsur- face changes in water storage.
Show more

9 Read more

Multi decadal hydrologic change and variability in the Amazon River basin: understanding terrestrial water storage variations and drought characteristics

Multi decadal hydrologic change and variability in the Amazon River basin: understanding terrestrial water storage variations and drought characteristics

Abstract. We investigate the interannual and interdecadal hydrological changes in the Amazon River basin and its sub- basins during the 1980–2015 period using GRACE satellite data and a physically based, 2 km grid continental-scale hy- drological model (LEAF-Hydro-Flood) that includes a prog- nostic groundwater scheme and accounts for the effects of land use–land cover (LULC) change. The analyses focus on the dominant mechanisms that modulate terrestrial water storage (TWS) variations and droughts. We find that (1) the model simulates the basin-averaged TWS variations remark- ably well; however, disagreements are observed in spatial patterns of temporal trends, especially for the post-2008 pe- riod. (2) The 2010s is the driest period since 1980, charac- terized by a major shift in the decadal mean compared to the 2000s caused by increased drought frequency. (3) Long-term trends in TWS suggest that the Amazon overall is getting wetter (1.13 mm yr −1 ), but its southern and southeastern sub- basins are undergoing significant negative TWS changes, caused primarily by intensified LULC changes. (4) Increas- ing divergence between dry-season total water deficit and TWS release suggests a strengthening dry season, especially in the southern and southeastern sub-basins. (5) The sub- surface storage regulates the propagation of meteorological droughts into hydrological droughts by strongly modulating TWS release with respect to its storage preceding the drought condition. Our simulations provide crucial insight into the importance of sub-surface storage in alleviating surface wa- ter deficit across Amazon and open pathways for improving prediction and mitigation of extreme droughts under chang-
Show more

22 Read more

Interannual variations of the terrestrial water storage in the Lower Ob' Basin from a multisatellite approach

Interannual variations of the terrestrial water storage in the Lower Ob' Basin from a multisatellite approach

Remote sensing techniques have been very useful for studying cold region climate and hydrology (Massom, 1995; Smith, 1997; Seidel and Martinec, 2004) as they provide a unique mean to observe large regions. Good capabili- ties for monitoring snow extent and depth using passive mi- crowave measurements (Yang et al., 2002; Grippa et al., 2005) or multispectral images (Hall et al., 2002; Robinson and Frei, 2000), water levels and discharges using radar al- timetry (Kouraev et al., 2005), and inundation extent com- bining multisatellite information (Papa et al., 2007, 2008a) have already been demonstrated. The Gravity Recovery And Climate Experiment (GRACE) mission, launched in 2002, detects tiny changes in the Earth’s gravity field which can be related to the spatio-temporal variations of the terrestrial wa- ter storage (TWS) at monthly or 10-day time-scales (Tapley et al., 2004). Previous studies provide important information on changes in TWS and snow mass at high latitudes (Muskett and Romanovsky, 2009; Frappart et al., 2010). TWS, repre- senting an integrated measurement of the water stored in the different hydrological reservoirs, and consequently, the sum of the surface water, water stored in the root zone, snowpack and groundwater, can be considered as a good indicator of the changes that occur in the hydrological conditions globally, and at basin-scale. Nevertheless, TWS is difficult to measure due to the lack of a complete network of in situ observa- tions of the terrestrial hydrological components. The hydro- logic regime of rivers is strongly influenced by the presence of permafrost at high latitudes. The river basins with high permafrost coverage have lower subsurface storage capacity, which causes a lower winter baseflow and a higher summer peak flow, than basins with low coverage (Woo, 1986; Kane, 1997; Smith et al., 2007).
Show more

11 Read more

Water storage changes and climate variability within the Nile Basin between 2002 and 2011

Water storage changes and climate variability within the Nile Basin between 2002 and 2011

J.L. Awange acknowledges the financial support of the Alexander von Humbodlt Foundation (Ludwig Leich- hardt’s Memorial Fellowship), The Institute for Geoscience Research (TIGeR), and a Curtin Research Fellowship that supported his stay in Karlsruhe (Germany) and Perth (Australia), the period during which parts of this study was undertaken. He is grateful for the warm welcome and the conducive working atmosphere provided by his host Prof. Heck at the Geodetic Institute, Karlsruhe Institute of Technology (KIT). E. Forootan and J. Kusche are grate- ful for the financial support by the German Research Foundation (DFG) under the project BAYESG. The authors are grateful to the GRACE-GFZ, GLDAS, TRMM, altimetry data, and climate indices used in this study. We also thank A. Ahunegnaw for Fig. 2, and J. Boy, M. Rodell, M. Sultan, and S. Swenson for their valuable comments on the manuscript during the AGU2011 Chapman Conference on Remote Sensing of Terrestrial Waters in Hawaii, USA. This work is a TIGeR publication (no. 568).
Show more

19 Read more

Statistical prediction of terrestrial water storage changes in the Amazon Basin using tropical Pacific and North Atlantic sea surface temperature anomalies

Statistical prediction of terrestrial water storage changes in the Amazon Basin using tropical Pacific and North Atlantic sea surface temperature anomalies

from climate models often have low to moderate skill in the region starting from a 1-month lead time, as a consequence of uncertainties in initial conditions and incomplete represen- tation of convection and other atmospheric processes (e.g., Lavers et al., 2009). In turn, global hydrology and land sur- face models often have difficulties representing soil mois- ture in deeper soil layers (Zeng, 1999) and surface water dy- namics in rivers, lakes, and floodplains (Swenson and Milly, 2006; Han et al., 2010; Werth and Güntner, 2010). Important uncertainties also remain in our understanding of biosphere– atmosphere interactions, including the role of deeply rooted trees in modulating seasonal and interannual variability in regional climate (Lee et al., 2005; Golding and Betts, 2008) and the impacts of fire-emitted aerosols on radiation and cir- culation (Tosca et al., 2013). In this context, investments in both statistical and dynamical forecasting approaches have the potential to advance the field. For statistical models, this may occur through extraction of key mechanisms and tele- connections regulating variability in hydrological cycle pro- cesses (and also by serving as a benchmark for forecasts from other, more complex models). Dynamical model forecasts, in contrast, are likely to become increasingly robust with ad- vances in climate modeling, increases in resolution, and im- proved estimates of initial conditions (Barnston et al., 2012; van Dijk et al., 2013). These models also are more likely to maintain their fidelity during periods of rapid Earth system change since they simulate the complete evolving state of ocean–atmosphere conditions.
Show more

14 Read more

Recent changes in terrestrial water storage in the Upper Nile Basin: an evaluation of commonly used gridded GRACE products

Recent changes in terrestrial water storage in the Upper Nile Basin: an evaluation of commonly used gridded GRACE products

Abstract. GRACE (Gravity Recovery and Climate Experi- ment) satellite data monitor large-scale changes in total ter- restrial water storage (1TWS), providing an invaluable tool where in situ observations are limited. Substantial uncer- tainty remains, however, in the amplitude of GRACE grav- ity signals and the disaggregation of TWS into individual terrestrial water stores (e.g. groundwater storage). Here, we test the phase and amplitude of three GRACE 1TWS sig- nals from five commonly used gridded products (i.e. NASA’s GRCTellus: CSR, JPL, GFZ; JPL-Mascons; GRGS GRACE) using in situ data and modelled soil moisture from the Global Land Data Assimilation System (GLDAS) in two sub-basins (LVB: Lake Victoria Basin; LKB: Lake Kyoga Basin) of the Upper Nile Basin. The analysis extends from January 2003 to December 2012, but focuses on a large and accurately ob- served reduction in 1TWS of 83 km 3 from 2003 to 2006 in the Lake Victoria Basin. We reveal substantial variability in current GRACE products to quantify the reduction of 1TWS in Lake Victoria that ranges from 80 km 3 (JPL-Mascons) to 69 and 31 km 3 for GRGS and GRCTellus respectively. Rep- resentation of the phase in TWS in the Upper Nile Basin by GRACE products varies but is generally robust with GRGS, JPL-Mascons, and GRCTellus (ensemble mean of CSR, JPL, and GFZ time-series data), explaining 90, 84, and 75 % of the variance respectively in “in situ” or “bottom-up” 1TWS in the LVB. Resolution of changes in groundwater storage (1GWS) from GRACE 1TWS is greatly constrained by
Show more

17 Read more

Large-scale total water storage and water flux changes over the arid and semiarid parts of the Middle East from GRACE and reanalysis products

Large-scale total water storage and water flux changes over the arid and semiarid parts of the Middle East from GRACE and reanalysis products

Abstract Previous studies indicate that water storage over a large part of the Middle East has been decreased over the last decade. Variability in the total (hydrological) water flux (TWF, i.e., precipitation minus evapotranspiration minus runoff) and water storage changes of the Tigris–Euphrates river basin and Iran’s six major basins (Khazar, Persian, Urmia, Markazi, Hamun, and Sarakhs) over 2003–2013 is assessed in this study. Our investigation is performed based on the TWF that are estimated as temporal derivatives of terrestrial water storage (TWS) changes from the Gravity Recovery and Climate Experi- ment (GRACE) products and those from the reanalysis products of ERA-Interim and MERRA-Land. An inversion approach is applied to consistently estimate the spatio-tem- poral changes of soil moisture and groundwater storage compartments of the seven basins during the study period from GRACE TWS, altimetry, and land surface model products. The influence of TWF trends on separated water storage compartments is then explored. Our results, estimated as basin averages, indicate negative trends in the maximums of TWF peaks that reach up to -5.2 and -2.6 (mm/month/year) over 2003–2013, respectively, for the Urmia and Tigris–Euphrates basins, which are most likely due to the reported mete- orological drought. Maximum amplitudes of the soil moisture compartment exhibit neg- ative trends of -11.1, -6.6, -6.1, -4.8, -4.7, -3.8, and -1.2 (mm/year) for Urmia, Tigris–Euphrates, Khazar, Persian, Markazi, Sarakhs, and Hamun basins, respectively.
Show more

25 Read more

Data assimilation of GRACE terrestrial water storage estimates into a regional hydrological model of the Rhine River basin

Data assimilation of GRACE terrestrial water storage estimates into a regional hydrological model of the Rhine River basin

Abstract. The ability to estimate terrestrial water storage (TWS) realistically is essential for understanding past hy- drological events and predicting future changes in the hydro- logical cycle. Inadequacies in model physics, uncertainty in model land parameters, and uncertainties in meteorological data commonly limit the accuracy of hydrological models in simulating TWS. In an effort to improve model performance, this study investigated the benefits of assimilating TWS es- timates derived from the Gravity Recovery and Climate Ex- periment (GRACE) data into the OpenStreams wflow_hbv model using an ensemble Kalman filter (EnKF) approach. The study area chosen was the Rhine River basin, which has both well-calibrated model parameters and high-quality forcing data that were used for experimentation and compar- ison. Four different case studies were examined which were designed to evaluate different levels of forcing data qual- ity and resolution including those typical of other less well- monitored river basins. The results were validated using in situ groundwater (GW) and stream gauge data. The analy- sis showed a noticeable improvement in GW estimates when GRACE data were assimilated, with a best-case improve- ment of correlation coefficient from 0.31 to 0.53 and root mean square error (RMSE) from 8.4 to 5.4 cm compared to the reference (ensemble open-loop) case. For the data-sparse case, the best-case GW estimates increased the correlation coefficient from 0.46 to 0.61 and decreased the RMSE by
Show more

22 Read more

Trend dynamics of GRACE terrestrial water storage in the Nile River Basin

Trend dynamics of GRACE terrestrial water storage in the Nile River Basin

Abstract: GRACE-derived Terrestrial Water Storage Anomalies (TWSA) continue to be used in an expanding array of studies to analyze numerous processes and phenomena related to terrestrial water storage dynamics, including groundwater depletions, lake storage variations, snow, and glacial mass changes, as well as floods, droughts, among others. So far, however, few studies have investigated how the factors that affect total water storage (e.g., precipitation, runoff, soil moisture, evapotranspiration) interact and combine over space and time to produce the mass variations that GRACE detects. This paper is an attempt to fill that gap and stimulate needed research in this area. Using the Nile River Basin as case study, it explicitly analyzes nine hydroclimatic and anthropogenic processes, as well as their relationship to TWS in different climatic zones in the Nile River Basin. The analytic method employed the trends in both the dependent and independent variables applying two geographically multiple regression (GMR) approaches: (i) an unweighted or ordinary least square regression (OLS) model in which the contributions of all variables to TWS variability are deemed equal at all locations; and (ii) a geographically weighted regression (GWR) which assigns a weight to each variable at different locations based on the occurrence of trend clusters, determined by Moran’s cluster index. In both cases, model efficacy was investigated using standard goodness of fit diagnostics. The OLS showed that trends in five variables (i.e., precipitation, runoff, surface water soil moisture, and population density) significantly (p<0.0001) explain the trends in TWSA for the basin at large. However, the models R2 value is only 0.14. In contrast, the GWR produced R2 values ranging between 0.40 and 0.89, with an average of 0.86 and normally distributed standard residuals. The models retained in the GWR differ by climatic zone. The results showed that all nine variables contribute significantly to the trend in TWS in the Tropical region; population density is an important contributor to TWSA variability in all zones; ET and Population density are the only significant variables in the semiarid zone. This type of information is critical for developing robust statistical models for reconstructing time series of proxy GRACE anomalies that predate the launch of the GRACE mission and for gap-filling between GRACE and GRACE-FO.
Show more

19 Read more

Water storage changes and balances in Africa observed by GRACE and hydrologic models

Water storage changes and balances in Africa observed by GRACE and hydrologic models

Continental water storage plays a major role in Earth's climate system. However, temporal and spatial variations of continental water are poorly known, particularly in Africa. Gravity Recovery and Climate Experiment (GRACE) satellite mission provides an opportunity to estimate terrestrial water storage (TWS) variations at both continental and river-basin scales. In this paper, seasonal and secular variations of TWS within Africa for the period from January 2003 to July 2013 are assessed using monthly GRACE coefficients from three processing centers (Centre for Space Research, the German Research Centre for Geo- sciences, and NASA's Jet Propulsion Laboratory). Monthly grids from Global Land Data Assimilation System (GLDAS)-1 and from the Tropical Rainfall Measuring Mission (TRMM)- 3B43 models are also used in order to understand the reasons of increasing or decreasing water storage. Results from GRACE processing centers show similar TWS estimates at seasonal timescales with some differences concerning inter-annual trend variations. The largest annual signals of GRACE TWS are observed in Zambezi and Okavango River basins and in Volta River Basin. An increasing trend of 11.60 mm/a is found in Zambezi River Basin and of 9 mm/a in Volta River Basin. A phase shift is found between rainfall and GRACE TWS (GRACE TWS is preceded by rainfall) by 2e3 months in parts of south central Africa. Comparing GLDAS rainfall with TRMM model, it is found that GLDAS has a dry bias from TRMM model.
Show more

11 Read more

Variability of Future Rainfall over the Mono River Basin of West Africa

Variability of Future Rainfall over the Mono River Basin of West Africa

It is thus common that the developing countries’ low-income populations are likely to be affected by factors related to global warming, as West Africa one of the regions in the world that are most vulnerable to climate change. This is par- ticularly true for rural areas in West Africa where agriculture is the most promi- nent instrument for securing income and overcoming poverty. This region ex- periencing exponential population growth is already facing the consequences of climate change through gradual land degradation and loss of croplands and ecosystem services [5] [6] and high water stress and scarcity year [7], along with recurrent and localized droughts and flash floods year [8]. These conditions, ex- pected to be exacerbated in the future, constitute significant threats to water re- sources, energy, agricultural activities and ecosystem services.
Show more

19 Read more

More frequent flooding? Changes in flood frequency in the Pearl River basin, China, since 1951 and over the past 1000 years

More frequent flooding? Changes in flood frequency in the Pearl River basin, China, since 1951 and over the past 1000 years

Abstract. Flood risks across the Pearl River basin, China, were evaluated using a peak flood flow dataset covering a period of 1951–2014 from 78 stations and historical flood records of the past 1000 years. The generalized extreme value (GEV) model and the kernel estimation method were used to evaluate frequencies and risks of hazardous flood events. Results indicated that (1) no abrupt changes or sig- nificant trends could be detected in peak flood flow series at most of the stations, and only 16 out of 78 stations exhib- ited significant peak flood flow changes with change points around 1990. Peak flood flow in the West River basin in- creased and significant increasing trends were identified dur- ing 1981–2010; decreasing peak flood flow was found in coastal regions and significant trends were observed dur- ing 1951–2014 and 1966–2014. (2) The largest three flood events were found to cluster in both space and time. Gener- ally, basin-scale flood hazards can be expected in the West and North River basins. (3) The occurrence rate of floods in- creased in the middle Pearl River basin but decreased in the lower Pearl River basin. However, hazardous flood events were observed in the middle and lower Pearl River basin, and this is particularly true for the past 100 years. However, precipitation extremes were subject to moderate variations
Show more

17 Read more

Decomposition analysis of water footprint changes in a water limited river basin: a case study of the Haihe River basin, China

Decomposition analysis of water footprint changes in a water limited river basin: a case study of the Haihe River basin, China

The scale effect (E(1m), 4.8 × 10 10 m 3 ) was the main contributor to the WF increase, equaling 380.1 % of the final 1T . E(1m) in all 17 sectors grew; the top 3 were agriculture (2.8 × 10 10 m 3 ); electricity, heat, and water (4.5 × 10 9 m 3 ); and the chemical industry (2.5 × 10 9 m 3 ), respectively equal- ing 57.7, 9.3, and 5.1 % of the total change in E(1m). E(1m) made different proportional contributions to the WF changes in different sectors. The increases in E(1m) make up more than 100 % of the total changes, especially in the sectors of wood, paper, and others (27 072.6 %); non- metallic mineral products (1007.5 %); and textile, clothing, and leather products (935.5 %). The increased contribution of E(1m) was mainly related to population growth and dras- tic demand expansion. From 2002 to 2007, the population of the HRB increased at the rate of 9.2 ‰ per year, much higher than the national average rate of 4.8 ‰ per year, and the scale of final demand soared from 2.4 × 10 12 RMB year −1 to 6.7 × 10 12 RMB year −1 (Beijing Statistics Bureau, 2003, 2008; Tianjin Statistics Bureau, 2003, 2008; Hebei Statis- tics Bureau, 2003, 2008; National Bureau of Statistics, 2003, 2008), which made the contribution of scale effect to the total WF increase. Because population and living standards keep increasing (National Bureau of Statistics, 2008; Haihe River Water Conservancy Commission, 2011), the scale effect may put more pressure on water resources in the future.
Show more

11 Read more

A simple groundwater scheme in the TRIP river routing model: global off line evaluation against GRACE terrestrial water storage estimates and observed river discharges

A simple groundwater scheme in the TRIP river routing model: global off line evaluation against GRACE terrestrial water storage estimates and observed river discharges

Figure 7 summarizes the comparison between simulated and GRACE 1TWS using the time correlation and RMSE. NOGW is well correlated with GRACE in tropical re- gions (Amazon, Congo or Ganges-Brahmaputra basins), in the Siberian Plains, in Europe and over some places in North America, while correlation is weak over desert re- gions such as the Sahel or the Gobi Desert (Fig. 7a). Con- versely, the RMSE scores are poor over tropical regions, while arid regions present relatively good scores (Fig. 7b). Figure 7c shows the correlation difference between the GW and NOGW simulated 1TWS. GW is globally better, espe- cially over the Paran´a, the Amazon and the Congo basins, and also in Europe and over the downstream part of the Mis- sissippi basin. Deteriorations are, however, found in Arctic regions along the Ob, Lena and Mackenzie basins, and also in a small region in the western part of the United States. These conclusions also apply to the correlation differences of the 1TWS monthly anomalies (Fig. 7e). These results sug- gest some defect in the groundwater parameterization, which will be discussed later. In Fig. 7d, groundwater improves the RMSE over the downstream Amazon, in Central Asia and also in Europe. Conversely, the RMSE scores are deteriorated over the Congo, Ganges and upstream Amazon basins. Else- where, no significant changes appear. The same conclusions can be drawn for the monthly anomaly RMSE differences shown in Fig. 7f, even though the improvements are globally less pronounced.
Show more

20 Read more

Climate and basin drivers of seasonal river water temperature dynamics

Climate and basin drivers of seasonal river water temperature dynamics

umented that AT and WT are both influenced by similar climatic drivers (e.g. incoming radiation), and tend towards thermodynamic equilibrium (Caissie, 2006). Both variables consequently tend to co-vary positively, making AT a very useful predictor (as it has been widely demonstrated in the literature; e.g. Webb and Nobilis, 1997), although the asso- ciation is only partly causal (Johnson, 2003). SWR (insola- tion from sun) is physically a positive input of energy; and it is appropriately captured in the models with positive co- efficients. In this study, LWR is the downward component of long-wave radiation (see Table 2). From an energy budget perspective, LWR therefore corresponds to a positive flux to- ward the river water. Consequently, LWR contribution to WT should be positive. Results (Table 3 and Fig. 5) show this is not necessarily the case. LWR corresponds to radiation diffused by clouds, and therefore co-varies positively with cloud cover (in addition, a pairwise plot of the study dataset shows that within a given season LWR inversely co-varies with SWR). Therefore, the negative WT–LWR associations would either be due to LWR acting as a proxy for processes driving colder water temperatures (e.g. cloud cover), or be a model artefact due to the LWR–SWR collinearity. SH rep- resents the mass of water vapour in moist air. The rate of evaporation at the water surface is directly proportional to the SH gradient (the more humid the air, the lower the evap- oration rate). All models give a positive association between SH and WT. As SH increases, the evaporation rate decreases, and consequently, cooling due energy loss as latent heat de- creases as well. WS has a cooling effect by increasing evap- oration at the water surface, which would be captured by a negative contribution to WT. In addition, WS plays a signif- icant role in air–water energy exchanges by increasing mix- ing, which would manifest as increased cooling or warming depending on the AT–WT gradient. For all models but au- tumn, WS has an overall negative contribution (cooling). For the autumn model, the variable RI and its percentage con- tribution are both low, so the positive association has to be considered with caution. P have positive or negative coeffi- cients depending on model. When rainfall occurs, its temper- ature may be higher or lower than that of the river depending on season. In addition, P can also act as a proxy for cloud cover, thus for reduced SWR and increased LWR; in some cases it might also capture the effect of increased streamflow and thermal inertia. P has limited importance and percent- age contribution in all the models, which is probably due to precipitations being event-based, whereas other variables are continuous (e.g. AT).
Show more

17 Read more

Modeling Climate-Fire Connections within the Great Basin and Upper Colorado River Basin, Western United States

Modeling Climate-Fire Connections within the Great Basin and Upper Colorado River Basin, Western United States

Given the importance of antecedent cli- mate in determining fire danger, we used the cross-correlation function (Venables and Rip- ley 2002) to examine synchronous and lagged correlations between SCPDSI and multiple broad scale synoptic patterns, including the North American Monsoon, El Niño Southern Oscillation (ENSO), Pacific Decadal Oscilla- tion (PDO), and 500 hPa geopotential height anomalies. No significant correlations were found between these synoptic patterns and SCPDSI within the study area. Wise (2010) describes a ‘Precipitation Dipole Transition Zone.’ This transition zone lies between two regions (the southwestern US and Pacific Northwest) that are highly affected by these larger patterns, but in opposite directions. For example, a positive ENSO anomaly is typical- ly associated with decreased cool season pre- cipitation in the southwestern US, but is also associated with increased cool season precipi- tation in the northwestern US. Since a large portion of our study region lies in this transi- tion zone, synoptic patterns do not have a clear impact on climate, and are unlikely to have strong correlations with fire activity. Also, re- lationships between fire and synoptic indices, like those found by Collins et al. (2006), may not be apparent due to the limited length of the MTBS time series.
Show more

12 Read more

Teleconnection analysis of runoff and soil moisture over the Pearl River basin in Southern China

Teleconnection analysis of runoff and soil moisture over the Pearl River basin in Southern China

The VIC-model’s daily simulation results are compared with the observations at a monthly scale after aggregation of daily data. The available streamflow observations at 10 gaug- ing stations (i.e., Gaoyao, Shijiao, Boluo, Zhedong, Baise, Nanning, Liuzhou, Wuzhou, Xinfengjiang, and Longchuan) in the basin (see Fig. 1) are used (Niu and Chen, 2010). The monthly scale is chosen for (1) the more “acceptable” accu- racy of the model simulation results, and (2) the compatibil- ity with the large-scale climate indices data. Table 1 presents a comparison between the observations and the model simu- lations of streamflow data for these 10 stations, by employ- ing three objective functions (i.e., relative bias – RB, relative root mean square error – RRMSE, and Nash–Sutcliffe effi- ciency – NSE – coefficient). The comparison suggests that the VIC model can simulate reasonably well the streamflow from the North River and the West River with its several sub-basins. However, there is a considerable discrepancy be- tween the streamflow simulations and the observations for the Boluo station in the East River. The studies by Niu and Chen (2010) and Wu and Chen (2012) have revealed that the Boluo streamflow is heavily regulated by the reservoirs in the upstream of the station. Therefore, the observations without the reservoir influences from two upstream stations (Xinfengjiang and Longchuan) are also used herein to eval- uate the streamflow simulations in the East River basin. The new results for the East River basin are comparable to the re- sults for the other stations in the North or West River basins (see Table 1). Based on the performance ratings suggested by Moriasi et al. (2007), the streamflow simulations at a monthly time step in the Pearl River basin in this study are evaluated as “satisfactory” (NSE > 0.5 and RB < ±0.25). With the val- idation of the VIC model performance, the monthly time se- ries of runoff and soil moisture are further aggregated for the 10 sub-basins (see Fig. 1 for their locations), and the wavelet- based analysis is carried out for the monthly runoff and soil
Show more

19 Read more

Teleconnection analysis of runoff and soil moisture over the Pearl River basin in southern China

Teleconnection analysis of runoff and soil moisture over the Pearl River basin in southern China

The VIC-model’s daily simulation results are compared with the observations at a monthly scale after aggregation of daily data. The available streamflow observations at 10 gaug- ing stations (i.e., Gaoyao, Shijiao, Boluo, Zhedong, Baise, Nanning, Liuzhou, Wuzhou, Xinfengjiang, and Longchuan) in the basin (see Fig. 1) are used (Niu and Chen, 2010). The monthly scale is chosen for (1) the more “acceptable” accu- racy of the model simulation results, and (2) the compatibil- ity with the large-scale climate indices data. Table 1 presents a comparison between the observations and the model simu- lations of streamflow data for these 10 stations, by employ- ing three objective functions (i.e., relative bias – RB, relative root mean square error – RRMSE, and Nash–Sutcliffe effi- ciency – NSE – coefficient). The comparison suggests that the VIC model can simulate reasonably well the streamflow from the North River and the West River with its several sub-basins. However, there is a considerable discrepancy be- tween the streamflow simulations and the observations for the Boluo station in the East River. The studies by Niu and Chen (2010) and Wu and Chen (2012) have revealed that the Boluo streamflow is heavily regulated by the reservoirs in the upstream of the station. Therefore, the observations without the reservoir influences from two upstream stations (Xinfengjiang and Longchuan) are also used herein to eval- uate the streamflow simulations in the East River basin. The new results for the East River basin are comparable to the re- sults for the other stations in the North or West River basins (see Table 1). Based on the performance ratings suggested by Moriasi et al. (2007), the streamflow simulations at a monthly time step in the Pearl River basin in this study are evaluated as “satisfactory” (NSE > 0.5 and RB < ±0.25). With the val- idation of the VIC model performance, the monthly time se- ries of runoff and soil moisture are further aggregated for the 10 sub-basins (see Fig. 1 for their locations), and the wavelet- based analysis is carried out for the monthly runoff and soil
Show more

18 Read more

Validation of terrestrial water storage variations as simulated by different global numerical models with GRACE satellite observations

Validation of terrestrial water storage variations as simulated by different global numerical models with GRACE satellite observations

ponent, the simulated snow variations in JSBACH already show smaller amplitude and negative phase differences com- pared with all the other models. This could be related to the fact that JSBACH simulates snow in a more physical way based on energy balance, which is totally different from the degree-day method applied by all the other models. The comparably better agreement of LSDM and WGHM with GRACE in terms of TWS in these snow-dominated basins is partly caused by the realistic surface water component rep- resented by these two models. In the dry catchments, the im- pact from AET on TWS is relatively strong. The smaller AET from MPI-HM also leads to better agreement with GRACE, whereas LSDM shows large differences with GRACE in terms of TWS, especially at some dry basins in central Africa, partly due to the overly simple evaporation scheme. PET is simulated using a superior parametrization by MPI- HM, while LSDM still applies the traditional Thornthwaite method based solely on air temperature. The groundwater considered by WGHM also has some impact on the simu- lated TWS, especially at basins such as Tocantins, Mekong, Niger and Mississippi. At the Yukon basin, we found the bad performance of all models in terms of TWS when compared with GRACE, which could be due to the effects of atmo- spheric and oceanic de-aliasing errors not further discussed in our current study. In future, we would like to assess all pos- sible errors of GRACE TWS through investigation of simu- lated GRACE-type gravity field time series (Flechtner et al., 2016) based on realistic orbits and instrument error assump- tions as well as background error assumptions out of the up- dated ESA Earth system model (Dobslaw et al., 2015, 2016), which we believe will further help to explain the discrep- ancy between global models of the terrestrial water cycle and GRACE satellite observations.
Show more

17 Read more

Show all 10000 documents...

Related subjects