The basin of the river Massa was selected for study. Table 3.1 displays the characteristics of this basin. This river is situated close to Zermatt, a town located in the Central Swiss Alps of the Canton of Valais at the southern end of the Matter Valley (MeteoSwiss). Zermatt is also the location in which shortwave radiation levels are recorded. The European Alps are one of the most intensively studied mountain ranges in the world (Haeberli & Beniston, 1998) and this region provides access to multiple weather and gauging stations which are situated at a variety of elevations with areas of permanent and seasonal snow cover. Decades of data are also available because of the continuous monitoring undertaken by numerous researchers. The Massa has been chosen as the Aletschgletscher is the most voluminous glacier in the Alps and is an indicator of long-term climate trends as it is not sensitive to short-term climate fluctuations in which smaller glaciers in
Table 3.1: Basin characteristics of the chosen study area, basin area (%) and basin glaciated (%).
River Basin area (km2) Basin glaciated (%)
Massa 195 65.9
the Alps have shown; such as the period of advance in the 1920s and 1980s (Jouvet et al., 2011).
The climatic conditions in the Matter valley have a continental character with low precipitation and high-radiation budgets (Randin et al., 2009). Average annual precipitation is only approximately 475 mm, which is one of the lowest in Switzerland. This low precipitation is due to the valley surrounded by high peaks that often exceed 4,000m a.s.l. in elevation (Hill, 2012). Canton Valais therefore is extremely reliant on glacial melt as a fresh water source thus studying the quality of this water and the forces controlling it is highly important.
The river Massa draining from Aletschgletscher is the primary focus of the study. Aletschgletscher is the largest glacier in the Alps with the basin measuring 195km2, 65.9% of which is glaciated. The gauging station in which
the water temperature and discharge measurements derive is situated 1458m a.s.l. (2.4km from the glacial portal), which is the lowest point of the basin that ranges up to Aletschhorn at 4194m a.s.l. The mean annual runoff (1957- 2005) of the basin is 2.112m (Collins, 2008). The river is approximately 7km long and passes through the Massa gorge and onwards into the Rhone. The basin areas (km2) and total glaciated area of the basin (%) for the study
areas are shown in Table 1.1. Almost two thirds of Massa’s basin is glaciated and it is Alpine and high Alpine in character it is also classed as a hydrological research basin by the Swiss National Hydrological and Geological Survey and therefore human interference is minimal (Braun and Renner, 1992). Figure 3.1 display maps of the study basins and region with the gauging stations added.
Figure 3.1: Map of Switzerland with Aletschgletscher basin and gauging locations. Zermatt also shown (Collins & Taylor, 1990).
3.3
Data acquisition
Hydrological data was gathered from the Swiss Federal Office of the Envi- ronment (FOEN); this method of data allows in depth analysis as it is at a high resolution and measurements are collected on the hour everyday for the whole year from a gauging station situated on the river. Local shortwave radiation data was not available at the Massa river site and therefore hourly measurements from Zermatt have been used. The possible implications of the unavailability of local shortwave radiation measurements to the Massa is that it will not express the true levels of radiation of the basin as the basin is situated at a higher altitude and approximately 45km away from Zermatt; however the radiation data will still show the temporal variations at a regi- onal scale. Continuous hourly data is also available for the years 2003-2012 which allows precise comparisons and time series with water temperature
and discharge.
3.4
Data analysis
The years 2003-2012 are analysed since there are complete and continuous annual records of radiation, water temperature and discharge measurements. Hourly measurements of discharge at Massa were processed into annual data sets for the calendar years 2003-2012 by manually selecting and separating data recorded into different years. Annual trends are analysed by calculating the mean, maximum, minimum and standard deviation of water temperature and discharge in order to assess trends between the parameters. This method of analysis has been used by Brown et al., (2006). Annual mean radiation will be analysed to signify the years with the highest and lowest totals. An objective is to analyse seasonal runoff and thermal regimes of the Massa, which is achieved by hydrographs of water temperature and discharge similar to those of Collins (2009); however both parameters are plotted on the same graph for a clearer illustration of potential relationships. The year 2012 is chosen to analyse seasonal, diurnal and daily measurements in depth as this is the most recent year with complete data available. Moreover previous studies have not analysed a year as recent as 2012. Seasonal radiation also is analysed, however this has high hourly fluctuations and therefore is processed into a series of weekly means so it can be compared with discharge and temperature.
Brown et al.,(2006) analyses hourly air temperature and water temperature over a weekly period, the same method of analysis is used in this thesis; however using shortwave radiation measurements not air temperature. This will contribute to the objective of understanding the diurnal and daily re- lationship between radiation and water temperature and also the control that radiation has on water temperature. To understand the level of flow at which stream temperatures cease to surge and decrease from the peak will be achieved by analysing the daily average water temperatures and outlining the point at which the decrease begins. This analysis will also contribute to the understanding why stream temperature decreases in late spring and early summer when radiation peaks.
4
Results
Annual, seasonal and diurnal analysis of radiation, discharge, water tempe- rature from the Massa river are presented in this section.
4.1
Annual trends
The average annual radiation for the years 2003-2012 is shown in Table 4.1. 2012 has the highest average radiation with 2004 having the lowest. As 2012 has the highest average annual radiation for the recorded years and is the latest year with complete data it shall be the year chosen to have further analysis. The monthly percentage of the total annual radiation for 2012 is displayed in Table 4.2. May, June, July and August have the highest percentages, with the year having 50.11% of the years total radiation. June has the highest percentage of 13.05% and December with the lowest of 2.49%. It was expected that June would have the highest total radiation due to it being the month of the summer solstice (20 June). Seasonal radiation levels follow that of a typical mid-latitude region.
Table 4.1: Mean radiation (W m−2) in Zermatt for the period 2003-2012. Year Mean 2003 162.45 2004 154.2 2005 157.75 2006 157.42 2007 158.7 2008 156.22 2009 164.19 2010 160.05 2011 161.78 2012 164.46
Table 4.2: Monthly percentage of total radiation and discharge for the year 2012.
Month % of total annual discharge % of total annual radiation
January 0.24 2.98 February 0.16 5.89 March 0.53 9.28 April 0.89 10.45 May 5.62 12.65 June 19.93 13.05 July 25.98 12.84 August 28.72 11.57 September 12.18 8.49 October 4.24 5.89 November 0.68 3.67 December 0.37 2.49
Annual records of discharge from Massa were processed and analysed for the years 2003 to 2012. Table 4.3 displays the mean annual discharge for each of these years. 2003 has the highest total discharge out of the 10 observed years; this year is recorded as a warm year due to central Europe suffering a heat wave. The all time Swiss heat record of 41.5◦C was set on 11 August, 2003 (Met Office, 2015). Massa follows a typical runoff regime of a highly glacierised Alpine basin. Between the months November and March discharge levels are at the winter minima due to there being little to no meltwater and
precipitation falling primarily as snow. Maximum discharge occurs through the months June-September known as the ablation period. Table 4.2 shows the percentage of the total annual discharge for each month in 2012 from the Massa, it has a typical flow regime of an Alpine glacial basin as 86.8% of the annual total discharge was in four months; June, July, August and September with the winter months accounting for less than 10% of annual runoff. August was the highest with 28.72% of the years discharge, February the lowest with 0.16%. Mean annual water temperature for the years 2003 to 2012 are show in Table 4.4. With the exception of 2010 there is a trend of years with higher discharge possessing lower water temperatures. The year 2003 demonstrates this relationship having the highest average discharge and also the lowest average water temperatures.
Table 4.3: Statistics of hourly discharge (m3s−1) of Massa for the period
2003-2012.
Year Mean Min Max Std. Dev.
2003 20.2 0.15 118.95 28.21 2004 14.49 0.2 95.24 19.18 2005 15.5 0.22 106.29 21.02 2006 15.07 0.06 109.07 21.26 2007 15.64 0.35 102.12 18.45 2008 15.5 0.28 108.73 21.81 2009 16.6 0.15 91.85 21.45 2010 14.2 0.19 109.12 20.55 2011 16.44 0.21 122.3 20 2012 15.96 0.14 120.82 21.28
Table 4.4: Statistics of hourly water temperature (◦C) of Massa for the period 2003-2012. The minimum temperature has not been included due all the observed years experiencing minima of 0◦C
Year Mean Max Std. Dev.
2003 0.89 4.28 0.51 2004 0.92 4.4 0.54 2005 0.92 4.32 0.55 2006 1.22 2.81 0.62 2007 1.18 4.41 0.57 2008 1.21 5.02 0.55 2009 1.15 4.89 0.53 2010 1.07 3.88 0.51 2011 0.93 3.82 0.46 2012 0.98 4.62 0.52
The seasonal hydrographs of water temperature (blue) and discharge (black) are shown on Figure 4.1 for the years 2003 (a) to 2012 (j). There is a similar pattern throughout the years with water temperature peaking between the Julian days 92 and 133. Figure 4.1 (j) displays the hourly data taken from the Massa, which illustrates the seasonal relationship between discharge (black) and water temperature (blue) over 2012. The hourly measurements for 2012 have been processed into seven day averages as seasonal trends for water temperature and discharge are to be analysed with radiation; which has a high diurnal range therefore this seven-day average smooths out the series for a clearer, clean observation. There is a clear apparent seasonal relationship between discharge and water temperature which can be identified throughout the years. Typically discharge is low during the winter months until the late ablation period where it rapidly increases from 7.35 m3s−1 in to the peak
of 120 m3s−1 in just 45 days. Discharge continues to increase through the summer until early August when it peaks then rapidly decreases over 80 days back to low levels of winter. Discharge decreases earlier than it would be expected. Water temperature on the other hand peaks in early May when discharge is still low, but from that point there is a gradual decrease until the end of summer. There are distinctive warm water pulses in March and April which can be observed in Figure 4.1. The relationship between water temperature and discharge follow that discussed previously in which the highest periods of discharge will show a response in water temperatures decreasing.
Figure 4.1: Seasonal variation of discharge (m3s−1) as the black series and
water temperature (◦C) as the blue series of the Massa for the years 2003 (a) to 2012 (j).
Analysing the relationship between seasonal water temperature, discharge and radiation is a key objective. The year 2012 was observed in depth due to it possessing the highest total radiation over the years and it is the most recent year with complete data (see Table 4.1). Hourly data has been pro- cessed into weekly averages to give a smoother series (Figure 4.2). The point of the summer solstice has been added also to outline the longest day of the year in terms of daylight. There is a clear curve in the radiation series across the year with the peak in the week of the summer solstice, which was ex- pected. In contrast water temperature peaks in late April, two months prior to radiation as it would be expected that a strong positive correlation would exist between these two parameters due to radiation being a major energy input in proglacial streams. This negative correlation occurs across ablation season as radiation is at its highest, and then water temperature gradually decreases after its peak. There is little response to these high radiation levels until the week of Julian day 287 where water temperature decreases at a higher rate back to the winter minima.
Figure 4.2: Seven day average of Massa water temperature (x20 ◦C) in blue, Zermatt radiation (W m−2) in red and discharge (m3s−1) in black of the year
2012 with the dashed line representing the summer solstice.
The monthly maximum, minimum, range and standard deviation of water temperature (◦C) for March-October 2012 for the Massa have been processed from hourly measurements (Table 4.5). The lowest maximum temperatures occur in June, July and August, which are regarded as the peak of the ablation season due to the highest temperatures. Additionally, these months host the lowest range which signify little diurnal variation in temperature. The highest maximum temperature and range occur in April, which is in the early ablation season; temperature and radiation have only begun to increase. With the range being so high this shows the month possesses a high diurnal variation in water temperature. This month shall be under close observation to analyse the diurnal variation between water temperature, radiation and discharge.
The seasonal relationship between discharge and radiation is more apparent as Figure 4.2 illustrates. This graph has been constructed with hourly mea- surements processed into weekly averages. As discussed radiation (red) peaks
in the week of the summer solstice which in 2012 was 20 June. In comparison, discharge has a greater rate of increase seasonally than radiation, with levels staying around the winter minima until mid-April in which the increase be- gins. Radiation however has a gradual rise beginning late January, with the seasonal curve clearly evident. A lag-time exists between these two parame- ters with the highest radiation values occurring prior to the peak discharge. Furthermore discharge is still climbing during the summer solstice and does not reach its peak until approximately 50 days later. Peak discharge for this year occurs when radiation is on the decrease, which shows that there is not an immediate response from discharge to radiation.
Table 4.5: Monthly minimum, maximum, range and standard deviation of water temperature (◦C) for the months March- October 2012.
Month Max Min Range Std. Dev.
March 2.79 0.14 2.65 0.47 April 4.62 0.53 4.19 0.61 May 2.35 0.5 1.84 0.37 June 1.68 0.85 0.83 0.15 July 1.57 0.75 0.82 0.14 August 1.73 0.78 0.95 0.18 September 1.74 0.64 1.11 0.2 October 2.12 0 2.12 0.42
An objective was to understand why water temperature decreases in the period when radiation is high. Water temperatures surge during the early ablation season. Figure 4.3 shows the daily average water temperature and discharge between the Julian days 91 and 152, which have been selected as this is the period in which discharge increases from its winter minima. In the period between days 91 and 116 there are large fluctuations in water temperature, but here in contrast discharge varies little and remains at a low level. Discharge begins to rise from the days 117 to 122, in response average daily water temperature decreases from 2.33◦C to 1.25◦C in just a period of 4 days. The trend is repeated as rising discharge shows a potential relationship with decreasing water temperatures; however temperature incre- ases as discharge decreases from the peak on Julian day 122, average daily discharge decrease from 6.78 m3s−1 to 3.67 m3s−1 on day 128, in the same
period water temperature increases from 1.36◦C to 1.84◦C. Towards the end of the observed period this trend is recognisable further, in this time frame water temperature does not surge. Furthermore stream temperature begins
to decrease as discharge continues to rise. Average daily radiation for the same period is shown in Figure 4.4, while there is much daily variation there is a clear steady increase as the added lines show. There does not appear to be a correlation with water temperature as expected.
Figure 4.3: Daily average of hourly water temperature (◦C) in blue and discharge (m3s−1) in black for the Massa between the Julian days 91 and
Figure 4.4: Daily average of hourly shortwave radiation (W m−2) with lines added to highlight the increase of radiation over the period between the Julian days 91 and 152, 2012.
In order to determine if the trends in Figures 4.3 and 4.4 were consistent for all the years between 2003-2012 the same analysis is demonstrated in Figure 4.5 and 4.6 but this has been produced with the hourly measurements for all the years 2003-2012 averaged to form a daily basis. There is less variation in the series which produces recognisable trend between discharge and water temperature. The tipping point at which water temperature stops increasing and then begins to decrease on Julian day 116 which in a regular year is April 26th. At this tipping point the discharge level is 3.54m3s−1. Radiation
however is still steadily rising throughout this period (Figure 4.6).
The level of discharge at which stream temperatures cease to surge and de- crease from the peak were determined by analysing the daily average water temperatures and outlining the point at which the decline begins. The total run off from that day and the annual total run off were calculated. Table 4.6 displays these results with the percentage of the annual total at which the daily total amounts. The highest percentages are in the years 2012 and 2006 with the lowest in 2008 and 2003. Water temperatures in 2008 decreased from the peak with only 0.02% of the annual discharge for that day while in
comparison 0.16% of the annual discharge was needed for water temperatures to respond in 2012. The percentage of the annual total discharge at which water temperatures decrease is shown in Table 4.7 for the years 2003-2012, which was calculated by the sum of the discharge from the start of the year up until the day stream temperatures decreases from the peak and cease to pulse.
Figure 4.5: Daily average of hourly water temperature (◦C) in blue and discharge (m3s−1) in black between the Julian days 91 and 152, 2003-2012.
Figure 4.6: Daily average of hourly shortwave radiation (W m−2) between
the Julian days 91 and 152, 2003-2012.
Table 4.6: Annual total discharge (106 m3) for the years 2003-2012 and the daily total of discharge from the day at which water temperature begins to decrease from the annual peak. With the percentage of the annual total added.
Year Annual total Daily total % of annual total
2003 636.52 0.19 0.03 2004 458.2 0.2 0.04 2005 488.85 0.48 0.1 2006 475.07 0.59 0.12 2007 453.97 0.27 0.06 2008 490.03 0.09 0.02 2009 523.49 0.17 0.03 2010 447.79 0.5 0.11 2011 518.45 0.16 0.03 2012 504.77 0.82 0.16
Table 4.7: Total discharge (106m3) from the January 1 up until the day water
temperature decreases and the percentage of the annual total.
Year Total prior to water temp decrease % of annual total
2003 5.32 0.84 2004 9.02 1.97 2005 8.42 1.72 2006 7.98 1.68 2007 4.43 0.98 2008 4.68 0.96 2009 7.24 1.38 2010 6.42 1.43 2011 2.91 0.56 2012 13.79 2.73
The Massa experiences warm pulses in the autumn and early winter (Figure 4.1). The Julian days 285-298 were observed closely as this period possessed the peak water temperatures for the post ablation season. The hourly variati- ons of discharge (black series) and water temperature (blue series) are shown in Figure 4.7. Discharge reduces at a high rate from 20.12m3s−1 for day
285 to 2.51m3s−1 on day 290, while in response water temperature fluctuates
Figure 4.7: Hourly variations of discharge (m3s−1) (black) and water tempe- rature (◦C) (blue) between the Julian days 285 and 298, 2012.
The hourly variation of radiation and stream temperature beginning Julian day 110 (19 April) leading up to the peak of water temperature on Julian day 117 (26 April) is shown in Figure 4.8. There is a potential pattern between both series with a lag time of a couple hours between peak radiation and peak stream temperature; however the daily maximum and minimum values express a relationship across the whole 8 days, suggesting that radiation is