P. van der Zaag

Mapping evapotranspiration trends using MODIS and SEBAL model in a data scarce and heterogeneous landscape in Eastern Africa

Evapotranspiration (ET) accounts for a substantial amount of the water use in river basins particular in the tropics and arid regions. However, accurate estimation still remains a challenge especially in large spatially heterogeneous and data scarce areas including the Upper Pangani River Basin in Eastern Africa. Using multitemporal Moderate-resolution Imaging Spectroradiometer (MODIS) and Surface Energy Balance Algorithm of Land (SEBAL) model, 138 images were analyzed at 250 m, 8 day scales to estimate actual ET for 16 land use types for the period 2008–2010. A good agreement was attained for the SEBAL results from various validations. For open water evaporation, the estimated ET for Nyumba ya Mungu (NyM) reservoir showed a good correlations (R?=?0.95; R2?=?0.91; Mean Absolute Error (MAE) and Root Means Square Error (RMSE) of less than 5%) to pan evaporation using an optimized pan coefficient of 0.81. An absolute relative error of 2% was also achieved from the mean annual water balance estimates of the reservoir. The estimated ET for various agricultural land uses indicated a consistent pattern with the seasonal variability of the crop coefficient (Kc) based on Penman-Monteith equation. In addition, ET estimates for the mountainous areas has been significantly suppressed at the higher elevations (above 2300 m a.s.l.), which is consistent with the decrease in potential evaporation. The calculated surface outflow (Qs) through a water balance analysis resulted in a bias of 12% to the observed discharge at the outlet of the river basin. The bias was within 13% uncertainty range at 95% confidence interval for Qs. SEBAL ET estimates were also compared with global ET from MODIS 16 algorithm (R?=?0.74; R2?=?0.32; RMSE of 34% and MAE of 28%) and comparatively significant in variance at 95% confidence level. The interseasonal and intraseasonal ET fluxes derived have shown the level of water use for various land use types under different climate conditions. The evaporative water use in the river basin accounted for 94% to the annual precipitation for the period of study. The results have a potential for use in hydrological analysis and water accounting.

AgriSuit : A web-based GIS-MCDA framework for agricultural land suitability assessment

A web-based framework (AgriSuit) that integrates various global data from different sources for multi-criteria based agricultural land suitability assessment based on the Google Earth Engine (GEE) platform is developed and presented. The platform enables online data gathering, training and classifying of land cover classes based on remote sensing and GIS techniques, as well as computation of suitability of land-use classes for agricultural activities. A demonstration of the framework on the Upper Blue Nile basin in Ethiopia is presented.

The management of international waters in EU and SADC compared

Abstract The paper draws on an international conference on the Management of Shared River Basins that was held in Maseru in May 1997 among representatives of SADC and EU member states. It uses the model of the ‘classical temple’ to analyse a number of case studies: the Zambezi, the Orange, the Incomati, the Limpopo, the Rhine, the Meuse and the Danube. The temple has as its foundation Integrated Water Resources Management. The roof, the shared management of international waters, is supported by three essential pillars that need to be level and equally strong: the political, institutional/legal and operational/technical pillars. It is concluded that the technical/operational pillar is central and crucial to build the temple and to keep it erect in periods of political or institutional instability.

Quantifying longitudinal land use change from land degradation to rehabilitation in the headwaters of Tekeze-Atbara Basin, Ethiopia

The spatiotemporal variability of the Land Use/Cover (LULC) is a strong influence on the land management and hydrological processes of a river basin. In particular in semi-arid regions like the Tekeze-Atbara (T-A) basin, accurate information about LULC change is a prerequisite for improved land and water management. The human-induced landscape transformations in the T-A basin, one of the main tributaries of the Nile River, were investigated for the last four decades (1972-2014). Separate LULC maps for the years 1972, 1989, 2001, and 2014 were developed based on satellite images, Geographic Information System (GIS) and ground information. Change detection analysis based on the transitional probability matrix was applied to identify systematic transitions among the LULC categories. The results show that >72% of the landscape has changed its category during the past 43years. LULC in the basin experienced significant shifts from one category to other categories by 61%, 47%, and 45%, in 1972-1989, 1989-2001, and 2001-2014, respectively. Although both net and swap (simultaneous gain and loss of a given LULC during a certain period) change occurred, the latter is more dominant. Natural vegetation cover, including forests, reduced drastically with the rapid expansion of crops, grazing areas and bare lands during the first two decades. However, vegetation started to recover since the 1990s, when some of the agricultural and bare lands have turned into vegetated areas. Forest land showed a continuous decreasing pattern, however, it has increased by 28% in the last period (2001-2014). In contrast, plantation trees have increased by 254% in the last three decades. The increase of vegetation cover is a result of intensive watershed management programs during the last two decades. The driving forces of changes were also discussed and rapid population growth and changing government policies were found to be the most important.

The evolution of regional cross-border water regimes, the case of Deltarhine

In this study, we look at the evolution of a cooperative water regime in the delta of the Rhine catchment. In a Dutch–German case study, we focus on cross-border cooperation on the local and regional scale, describing and analyzing how a remarkably resilient and robust transboundary water regime has evolved over the course of 50 years. Context-, interest- and knowledge-based explanations contribute important insights into the evolution of the Deltarhine regime, and it is shown that the legal, institutional and socio-economic context shapes and constrains regional cross-border cooperation. Surprisingly in this regard, we find that European water directives have not yet played a decisive, catalyzing role for policy harmonization across borders. Finally, we show that key individuals play a crucial role in regime formation and development. We suggest that the presence of entrepreneurs and leaders adds explanatory power to current conceptual frameworks in international river basin management, thus meriting further research.

Coupling land-use change and hydrologic models for quantification of catchment ecosystem services

Abstract Representation of land-use and hydrologic interactions in respective models has traditionally been problematic. The use of static land-use in most hydrologic models or that of the use of simple hydrologic proxies in land-use change models call for more integrated approaches. The objective of this study is to assess whether dynamic feedback between land-use change and hydrology can (1) improve model performances, and/or (2) produce a more realistic quantification of ecosystem services. To test this, we coupled a land-use change model and a hydrologic mode. First, the land-use change and the hydrologic models were separately developed and calibrated. Then, the two models were dynamically coupled to exchange data at yearly time-steps. The approach is applied to a catchment in South Africa. Performance of coupled models when compared to the uncoupled models were marginal, but the coupled models excelled at the quantification of catchment ecosystem services more robustly.