Are human activities responsible for hydrological drought?
Lay summary by Anna Scaini
In the future, climate change is expected to change precipitation distribution and increase temperatures. As a consequence, drought intensity and frequency will increase all over the world. Until now, human impact has been ignored in most projections for future hydrological drought. Are human activities related to the increase of drought? We need to start considering both human and climate impacts in future drought projections. For this purpose, we present a full global analysis of the impact of human activities (irrigation and reservoir regulation) on hydrological drought. Our objectives are:
(1) to describe the impact of human water use and reservoirs and
(2) how this impact varies regionally and seasonally.
Drought is induced when precipitation is below normal amounts. Lack of precipitation causes meteorological drought and consequently agricultural drought (lack of soil moisture). Hydrological drought usually originates after the occurrence of meteorological and agricultural droughts, because it is related to the way this deficiency is propagated through the hydrologic system. The groundwater levels will drop, resulting in lowering of the river levels, which results in a hydrological drought.
Our study presents for the first time the human impact on future hydrological droughts using the latest multi-model climate projections and multi-emission scenarios. The global hydrological and water resources model PCR-GLOBWB was used to simulate daily discharge for the period 1971–2099. Local water demand and reservoir operations are included in the human influences scenario.
Results at the global scale assess regions where humans have a larger impact than climate change impacts on future hydrological drought. Climate change is expected to increase drought intensity in large regions. Additionally, the characteristics of hydrological drought are impacted by water use and reservoir operations. This can vary depending on the local climate and available water resources. Results show an important impact of climate change and human water use in large parts of Asia, Middle East and the Mediterranean. In large regions of Asia, the impact of human water use on hydrological drought exceeds the local impact of climate change. The impact of climate change varies seasonally for parts of Europe and North-America. Climate change impact does not vary seasonally in North-Africa, Middle East and Mediterranean.
Scenario differences were studied for major river basins of the world. In general, it was found that human water use increases drought duration and severity. Drought intensity increased for all rivers except for the Mississippi and Danube. In these rivers, reservoirs allow water to be retained during the wet season and available in the dry season.
We demonstrate that human activities intensify hydrological drought. Human water use and reservoirs have large impacts on global hydrology and water resources. Our study demonstrates that we should include human water use and reservoirs in global hydrological models in order to improve the projections of future hydrological drought. This will significantly improve our understanding of future hydrology and help us ensure future water security.
For further information
Read the Journal of Hydrology original research article which this summary is based on Human and climate impacts on the 21st century hydrological drought (July 2015).
Visit the profile of the research ambassador, Anna Scaini, who wrote this summary.
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