Climate models have difficulties in predicting the frequency and intensity of future droughts on regional scales, possibly caused by inadequate representation of land surface hydrological processes. Vegetation is controlling the Earth's water and energy balance by transporting water from the subsurface to the atmosphere, through its roots. The water storage capacity in the vegetation's rootzone is a key parameter in predicting evaporation fluxes in land surface models because its size determines how long into the dry season vegetation is able to evaporate. Ecosystems design the size of their rootzone water storage reservoir to optimally function and to overcome dry periods, based on climatic conditions. Whereas climate is the major driver of root development, the rootzone storage capacity in the HTESSEL land surface scheme is only dependent on soil type and modelled soil depth. Moreover, the model describes root parameters by tables based on scarce observations of individual plants that do not represent ecosystem scales. This research aims to analyse the effect of the climate-based mass balance method for estimating the maximum water storage capacity in the vegetation's rootzone on the representation of water and energy fluxes in the HTESSEL land surface model. Maximum rootzone water storage capacities are estimated for 15 river catchments in Australia based on catchment-scale water balances. These estimates are implemented in the current surface parameterisation of the HTESSEL land surface model and offline simulations are performed. The current model performance and the model performance with adapted rootzone water storage capacities are evaluated regarding simulation of water and energy fluxes. According to this study, the storage capacity in the vegetation’s rootzone represented in HTESSEL is larger than the mass-balance derived estimates. The model strongly overestimates evaporation fluxes and thereby underestimates river discharge, with larger relative simulation errors in the dry season than in the wet season. The climate-based mass balance total rootzone water storage capacities have small effects on the representation of water and energy fluxes by the model, but contribute to a consistent improvement in predicting these fluxes. Nash Sutcliffe Efficiencies of the modelled river flows improve on average from 0.44 in the base model to 0.51 in the model with mass balance rootzone water storage capacities. The results indicate that the inadequate rootzone representation is a source of modelling error. However, it is expected that other hydrological process are also inadequately represented by the model, as the modelling simulation errors remain large when implementing mass balance rootzone water storage capacities. Moreover, it was found that internal vegetation dependent model parameters strongly influence the simulated fluxes and could therefore be another source of model bias. This study shows that investigating uncertainties in the representation of the rootzone in the HTESSEL land surface model is paramount. More research on the representation of hydrological processes in land surface models could lead to significant improvements in climate model predictions.

In Bangladesh, groundwater from shallow aquifers is used for communal drinking water supply on a large scale. This water is often polluted by naturally occurring arsenic, causing the largest scale poisoning through drinking water in the world (D. v. Halem, S. Bakker, G. Amy, & J. Van Dijk, 2009). In this report, a highly arsenic affected area in Bangladesh has been investigated. The main objective of this research is to obtain more insight in the three aspects of the DELTAP project: geology, water quality monitoring and safe water supply. It is aimed to analyse the relation between arsenic contamination and the local geology, to monitor the drinking water quality using mobile applications and to design and construct a water treatment unit. An important aspect of this research is to develop a monitoring and maintenance protocol in order to ensure safe water supply in the future. In the study area, 150 households have been selected and the water quality has been tested. The water quality has been assessed by measuring four chemical parameters and five physical parameters, using simple strip tests and mobile water quality applications. The results of the strip tests have been compared to the results of ICP-MS analysis in order to check the performance of the tests and the mobile apps. The arsenic and iron strip tests showed good performance. However, the manganese and mmonium strip tests did not perform well. Furthermore, no relations between the presence of arsenic and other chemicals have been found. It can be concluded that simple strip tests in combination with mobile applications are a promising tool for water quality monitoring, applying the Mobile Crowd Participation strategy. Since arsenic in groundwater has a geological origin, the relation between arsenic concentration in the groundwater and geology should be understood distinctly. In order to get a better understanding of this relationship, multiple tools and theories have been investigated and tested. Firstly, a geo information system has been used to map arsenic concentrations that have been obtained from the performed water quality tests. Based on the spatial analysis of the arsenic concentrations, three drillings have been performed: one drilling in a high, medium and low arsenic contaminated area. By use of the SASMIT tool, a link between sediment colour and arsenic contamination has been observed. Furthermore, geomorphological data and satellite images have been used to identify geological features in landscape which could also be linked to arsenic levels. The sediment colour found in drillings is in good accordance with the arsenic levels found in groundwater and thus, proves to be a useful tool to predict arsenic concentrations in the fieldwork area. However, the geological features in the research area are hard to identify and link to the measured arsenic concentrations. A water treatment unit has been designed and constructed in order to provide safe water to 5 to 10 households. Based on the iron and arsenic concentrations from the ICP-MS results and on practical considerations, a suitable location for the water treatment unit has been selected. The ratio of these parameters is important to remove arsenic from the groundwater efficiently. The water treatment unit is based on oxidation of arsenic along with iron and subsequent filtration with a rapid sand filter. Both chemical and biotic oxidation of arsenic and iron are ensured by setting up a biofilm carrier column before the rapid sand and anthracite filter unit. Finally, a parallel resin column has been installed to remove the residual arsenic. The water quality throughout the system varied substantially during the timeline of the project. The produced safe water at the end of the fieldwork did not meet the drinking water standards set by the WHO. Nevertheless, several recommendations have been provided and, in the future, more intensive backwash of the water treatment unit might be the key to produce and distribute safe water. Overall, a deeper knowledge on arsenic contamination and their effects have been achieved, and the improvement of the Bangladeshis live quality has been attempted.