Optimal Management Design of Irrigation and Related Resources: The case of Central Rift Valley Region, Ethiopia

Lemma Adane Truneh

Doctoral thesis

Abstract:

The Central Rift Valley Basin (CRVB) in Ethiopia is an endo hydrogenic basin, where climate, land use and land cover (LULC) changes have affected the water resources. They are the critical challenges that need to be addressed in the region. This study explores the impacts of climate and LULC changes on the major components of the water balance such as surface runoff (Q), water yield (WY) and evapotranspiration (ET) in the CRVB. The methodology followed integrated modelling approaches to simulate the impacts of climate and LULC changes on the components of the water balance to search for possible optimum irrigation water management options. In the analyses, representative concentration pathways (RCP) data derived by the MIROC5-RCA4 ensemble climate models were downscaled from the regional climate models (RCM) under coordinated regional downscaling experiment (CORDEX) for Africa (CORDEX - AFR - 44) and applied. Both historical and projected data of climate emission scenarios of RCP2.6, RCP4.5 & RCP8.5 were downscaled, bias corrected and used. The data sets from the climate scenarios were applied to SWAT models to analyze the conditions of the components of the water balance in the near term (2031-2060) and in the long-term (2070-2099) periods in the region. The CRVB was divided into three sub-basins (Ketar, Meki, & Shalla) based on their river systems, and their water balance components were simulated with Arc-SWAT models, calibrated, and validated by SWATCUPs in SUFI-2 algorithm. The models were calibrated with monthly flows from 1990 to 2001 and validated with flows from 2004 to 2010. The baseline simulation data run from 1984 to 2010 separately for each of the sub-basin. The annual variations due to the climate change impacts are varying in the maximum ranges from -65.4 % to +85.8 % in Q, from -42.2 % to +23.9 % in WY and from -4.1 % to +17.3 % in ET when compared to the annual values of the baseline data simulation outputs in the sub-basins. Water management interventions that reflect the identified site-specific water balance sensitivities were proposed. Regarding LULC change, integrated SWAT and Land Change Modeler (LCM) models were employed to evaluate the impacts of past and future LULC dynamics in the sub-basins. Past and future LULC analyses and predictions were done with LCM embedded in TerrSet 2020 software. LCM with a multi-layer perceptron (MLP) neural network for transition scenario analyses and a Markov chain method for predictions as well as SWAT model in fixing-changing methods for simulations were used to evaluate the conditions of hydrological processes for the LULC changes. LULC maps that represent past periods corresponding to the year 2003, 2008, 2013, 2020, and predicted maps of future periods for the years 2030, 2040 and 2050 were employed. The analyses resulted in an annual Q variation in the maximum ranges from -20.2 % to +32.3 %, WY from -10.9 % to +13.3 % and ET from -4.4 % to +14.4 % in the sub-basins due to the sole impacts of changes in LULC in comparison to the base LULC simulation outputs. The ranges of variation in the components of the water balance in each of the sub-basin due to the LULC changes were also huge and different. Based on the resulting simulation outputs, irrigation management options under climate and land use change dynamics were reviewed and proposed. The importance of water-irrigation-land use and climate change nexus synergies in relation to water requirement for agricultural purposes together with tradeoffs quantification for optimum or balanced resource use were also discussed. Further research on water-agriculture-land use and climate change nexus development approaches were recommended to manage their impacts on water resources and irrigation.

Keywords

Climate change, Land use and land cover change, Water balance, Nexus synergies, Optimum irrigation management

Language used: English

Date on which the thesis was submitted / produced: 17. 2. 2023

Thesis defence

• Supervisor: prof. Ing. Svatopluk Matula, CSc.

Czech University of Life Sciences Prague

Faculty of Agrobiology, Food and Natural Resources

Doctoral programme / field:
Agricultural Specialization / Exploitation and Conservation of Natural Resources