The world’s climate is changing. In the Netherlands one of the consequences is that water boards and municipalities are preparing for an increase in extreme precipitation. To evaluate the consequences in case of extreme precipitation all Dutch municipalities and water boards have to perform a stress test. In these stress tests the response of the water system is evaluated during extreme precipitation events which are much larger than the events used to design the water system. It is analysed which places are vulnerable to flooding and what risk (probability x potential damage) is involved. In the Netherlands the responsibility of different parts of the water system are with different government authorities. The municipality is responsible for the sewer system and the waterboard is responsible the surface water system. As a result both municipalities and waterboards often perform separate climate stress tests. Most of the time the municipality will not take the surface water into account or does it in a very simplified manner, for the waterboards this is vice versa. However, these systems do influence and hinder each other. This may result in an underestimation of the actual flooding, and corresponding damage. The aim of this research is to investigate to what extent the urban drainage system and the rural surface water system influence each other during extreme precipitation. In this research the case study area of Schijndel with the surrounding catchment area of the Schijndelse loop is analysed. The research must clarify if flooding caused by extreme precipitation is underestimated if the urban drainage system and the rural surface water system of Schijndel are analysed separately instead of combined. For this research a hydrodynamic model of the area is constructed in the hydrodynamic software package Infoworks ICM. The hydrodynamic model was used to investigate the difference between a coupled and separate model setup. The results show that the modelled flood locations correspond to known flood reports, but also that the difficult to determine infiltration rate, grid size and surface roughness significantly influence the model response. Nonetheless, the hydrodynamic model can be used to compare the response for short precipitation events between a coupled and separate sewer surface water model. The results show that flooding is underestimated if the sewer system and the surface water system are put to the test separately instead of combined. However, the differences are location and event specific and occur mainly just upstream and downstream of the combined sewer overflow locations in the study area. Here, the results show an increase in flood depth, flood duration, flood extent and the amount of houses flooded when the system is modelled coupled instead of separate. For future stress test studies it is recommended to schematize both the urban sewer system and surface water system together in one model, as this gives a better representation of the flow dynamics which occur in reality. ... Read more

IHE-Delft in cooperation with the Asian Development Bank (ADB) conducts a pilot project on assessing Crop Water Productivity in Asia, aiming to contribute to sustainable development in Asia’s irrigation sector, and create more value from scarce water resources. Indonesia is one of the 6 pilot countries where advanced technologies to measure Water Productivity (WP) from satellite data were introduced. Indonesia is the third largest rice producer of the world. Given the challenges such as growing population, degrading land and increasing water scarcity in upcoming decades, the Indonesian government aims to rehabilitate its irrigation systems. More insights in the spatial distribution of irrigation water and water productivity of rice paddies could contribute to decision-making in future rehabilitation investments.
This report describes the assessment of Water Productivity (WP) of paddy rice in Indonesia using the Surface Energy Balance Algorithm for Land (SEBAL). SEBAL is a tool that translates raw satellite measurements into maps of actual evapotranspiration and crop production, among others. The actual crop water consumption (i.e. actual evapotranspiration) and crop yield can now be estimated for every 30 m x 30 m, even if data on irrigation water application is not available. With this information, rice production per unit of land (kg/ha) as well as per unit of water consumed (kg/m3) can be computed.
Focus of this study are sites in Bali, West Java and Lombok. Fieldwork is conducted in Bali and West Java to support the maps with ‘ground truth’ data. Data is collected from local governmental institutes and farmers to verify the remote sensing outputs.
This research shows promising results linking SEBAL outputs with the ground truth even though the amount of fieldwork was limited. The inclusion of the new HANTS algorithm will create the technical opportunity to make daily WP reports for all rice fields in Indonesia, also under cloudy conditions. This could be a big information boost to support irrigation managers with their daily services of bringing water to farmers. Whereas some key explanatory reasons were detected (i.e. distance to canal, salt water intrusion, water quality, erosion), it is recommended to further explore relations between WP and influencing factors in the local context together with local irrigation officers. Even though the research revealed some limitations causing uncertainties, this new remote sensing technologies can support an efficient and effective investment purposes on modernization of irrigation. It is recommended that the Directorate of Irrigation and Lowlands recognize WP as a new policy instrument and implement it both at central level and irrigation district level.
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