Mapping root water uptake stress and carrying capacity using satellite observed soil moisture data

Brink, Herman (2014) Mapping root water uptake stress and carrying capacity using satellite observed soil moisture data.

Abstract:The waterboards responsibility for freshwater availability is managed by monitoring surface and ground water levels. These levels are influencing the soil moisture content in the soil, which is an important parameter for crop growing (root water uptake stress) and the carrying capacity. Knowledge of the soil moisture content can improve the management of the available water resources. In this research the soil moisture is retrieved from satellite observations and used to quantify the carrying capacity and root water uptake stress. Soil moisture is inhomogeneous over an area and can change rapidly in time due to atmospheric forcings (e.g. rainfall and evapotranspiration) and irrigation. Therefore fine resolution spatial and temporal soil moisture data are needed for good estimations of root water uptake stress and the carrying capacity at field scale. These fine spatial and temporal resolution data are produced by downscaling low spatial and high temporal Advance SCATerometer data (ASCAT, 12.5 km x 12.5 km, 1 day) with high spatial, low temporal resolution satellite data (RADARSAT-2, 25 m x 25m, 24 days). Four downscaling methods are applied and results are compared to in-situ soil moisture measurements of the soil moisture and soil temperature network located in the eastern part of the Netherlands for the year 2012. The downscaling method which uses a daily changing soil sensitivity parameter (β) shows the best fit between in-situ and satellite retrieved soil moisture data, using the ASCAT SWI 1 product for coarse resolution soil moisture, with correlation coefficients (R2) ranging up to 0.69 over the whole year. When only RADARSAT-2 observation dates are considered R2 increases even to 0.77. Maps of the retrieved soil moisture data show wet and dry areas at the expected locations. Grassland on peat in the western part of the study area presents a higher volumetric soil moisture content than high situated grasslands with sandy soils grounds in the east. The soil moisture values are transformed to a soil status using the Soil-Moisture-Stress indication (SMS-i) diagram. A SMS-i diagram is developed for each soil type of the Policy Analysis of Water Management for the Netherlands (PAWN) classification consisting of the combination of water or oxygen stress for root take up and the carrying capacity. Resulting SMS-i maps show that the contours of the different soil statuses are following the contours of the PAWN soil type map. This indicates that the soil status as defined in this research is more dominated by the soil type than by the retrieved volumetric soil moisture content. The status of the soil strongly depends on the soil type because i) each soil type has its own unique SMS-i diagram based on its water retention curve and ii) the coarse resolution satellite data has to be multiplied by the porosity of the soil to obtain the volumetric soil moisture content. The influence of the coarse resolution soil moisture data and the soil porosity are equal because their values are multiplied with each other in the used downscaling method. Because the used soil map, based on the Policy Analysis of Water Management for the Netherlands (PAWN) classification, has only 21 soil types for the Netherlands, soil properties are averaged and spatial heterogeneity within soil types is neglected. This research has shown that satellite retrieved data can be used to produce fine resolution soil moisture maps which can be translated to classes indicating the root water uptake stress and the carrying capacity. However, the average Mean Absolute Error of 0.08 m3/m3 over all grass covered in-situ stations after validation is high compared to the average porosity of 0.42. Accuracy and reliability of the retrieved maps should be improved to make them useful for operational water management.
Item Type:Essay (Master)
Faculty:ET: Engineering Technology
Subject:38 earth sciences
Programme:Civil Engineering and Management MSc (60026)
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