Challenges and opportunities for hydrological drought mitigation in the Anthropocene : the case of the Upper Tana Basin in Kenya

Abstract

Drought is a complex natural hazard that is increasingly causing major socio-economic and environmental losses across the globe. The arrival of the Anthropocene (human modified era) has complicated how the drought propagates from meteorological to hydrological. A number of recent studies have indicated that hydrological drought is not only caused by natural climate variability, but it is increasingly influenced and modified by human activities. Mitigating human induced or modified hydrological drought is a non-trivial challenge. In the light of this, this research presents a case study of a heavily modified catchment in Kenya, the Upper Tana basin. Kenya has experienced more than 30 droughts in the last 100 years, with the 2009-2011 drought event being the worst in 60 years. Using precipitation, temperature and runoff data (1976-2016), Standard drought indices, including SPEI/SPI and SRI, were used to characterize meteorological and hydrological droughts. Reservoir levels were also analysed. Drought features such as severity, lag, pooling, attenuation and lengthening, were identified. These are of practical importance to understanding drought impacts and mitigation options. A socio-hydrological framework was utilized to understand the feedbacks between the water users and hydrological droughts. This was done through qualitative study using semi-structured interviews, administered to 42 respondents, seeking to know how they were impacted by hydrological droughts and how they mitigated the impacts, as well as understanding any feedback loops. Results indicated a notable increase in frequency, severity and duration of meteorological and hydrological droughts from the 1990s. Satisfactory cross-correlation values of r, ~0.50, between SPI/SPEI and SRI, across the basin, at one month lag, indicated that it took one month for meteorological drought to be observed in the streamflow. The feedbacks resulting from the interplay between the water users and hydrological droughts revealed that measures implemented by the water users, aggravated the drought situation on the one hand, while others alleviated it. Unplanned consequences due to increased and unregulated surface and groundwater abstractions and cultivating on the riparian zone were identified. It was, however, not possible to ascertain the percentage with which human activities aggravate or alleviate hydrological drought impacts. This requires further research Monitoring of hydrological drought, in a human-influenced catchment like the Upper Tana basin, was a challenge due to limited institutional, human, knowledge and technological capacities, among others. Therefore, it is recommended that among the possible actions and approaches that a hydrological drought monitoring and early warning system is essential. In addition, monitoring of water demands against the available resources and proactive governance and regulating of human activities is recommended. Besides, the co-development of hydrological drought products and climate services, timely communication of hydrological drought information and bridging the gap between society, science (information providers) and politics is further recommended. This research contributes towards a foundation for further exploration of feedbacks between hydrological droughts and society in the Anthropocene. While this research was developed in the Upper Tana basin, the approach is equally applicable to other basins in the world. The research also contributes to the activities of the Scientific Decade (2013-2022), named “Phanta Rhei”, that promotes research activities that bridge the gap between the natural and social science (socio-hydrology) and between science and practice