Using remote sensing data of actual evapotranspiration in strategic and operational water level management

Holterman, R. (2015) Using remote sensing data of actual evapotranspiration in strategic and operational water level management.

Abstract:The regional water authorities are responsible for good water quantity conditions in their region, they do so by management of the surface water levels. Using remote sensing data to identify drought conditions can improve water level management to create better conditions for crop growth. The actual evapotranspiration (ETa) can be very different between areas, because it depends on the amount of water available in the soil. To make the best decisions in water level management it is important to know how ETa is distributed over the area to know exactly how much water shortage there is in different areas and to find out how to optimize water allocation. In this research, remote sensing data of ETa are used to assess the long-term drought conditions in the area of regional water authority Groot Salland and find out which areal characteristics have the most effect on drought. Also the short-term drought conditions were compared to the current water level management for several fixed drainage areas (FDAs) to find out if and how remote sensing data can be used to improve operational water level management. This research makes use of the Evaporative Stress Index (ESI), this index is a measure for the reduction in evapotranspiration from the potential evapotranspiration (ETp). An ESI of 0.10 indicates that ETa is 10 % less than ETp. The three year average ESI over the growing season of 2011, 2012 and 2013 was analyzed to find out which areal characteristics are explaining factors in the drought conditions seen. Four area characteristics were looked at. For altitude and freeboard (which is the difference between surface water level and ground surface level), the Pearson correlation was calculated and for land use and soil type the average ESI per category was calculated. The assessment shows that sandy soils suffer the most stress, followed by clay and peat. Forested areas suffer most stress, followed by urban/paved areas and grassland. Altitude and freeboard both show a weak positive correlation with ESI. This information has led to the creation of a drought vulnerability map, which can be used in determining strategic water level management. The drought vulnerability was determined using the findings of the statistical analysis. The drought vulnerability map can used in strategic water level management, to determine water level for new decrees or new target levels or to assess if water supply is going to the most vulnerable areas in times of need. Assessment of the operational water level management in 2013 shows that RS data of ETa can be useful for district managers and water level administrators and can help them to make better decisions in operational water level management. The information can also be used to inform farmers about drought conditions and help them to take decisions to irrigate. To compensate for the total evapotranspiration deficit by irrigation in 2013, the regional water authority would have had to supply almost double the amount of water than they did. To help district managers in their decision making the WGS drought monitor is introduced. The drought monitor shows, by using an easy to understand color coding system, how critical the drought condition in a certain area is. If published, the drought monitor could also be used by farmers to help them in deciding whether or not to irrigate their land. This research has shown that RS data can be very useful in improving water level management, it can be used to determine long-term drought conditions and determine drought vulnerability according to certain area characteristics. This research gives an indication of expected long-term drought vulnerability, for better and more accurate results a longer data record should be used. 5 Operational water level management can be improved if ESI would be available on a day to day basis, the drought monitor that has been introduced is a first step in what could be the development of an operational drought monitoring tool for WGS and other water authorities. This research suggests that water level management might not have as much effect on ESI as we would think, this indicates that ESI is very dependable on water input on land (i.e. precipitation or irrigation). To find out how much effect water level management has, further research is suggested in the form of a pilot area where one plot has a fixed water level throughout the growing season and one plot uses ESI as an input to adapt the water levels. This way the difference in average growing season ESI through adaptive water level management will be known. If the drought monitoring tool were to be used to give irrigation advice, further research should be done on the relationship between ESI and water input (through precipitation or irrigation).
Item Type:Essay (Master)
Faculty:ET: Engineering Technology
Subject:56 civil engineering
Programme:Civil Engineering and Management MSc (60026)
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