The purpose of this session is to review the state of scientific knowledge on tropical hydrology. The intertropical zone is the main energetic engine of climatic mechanics and can be characterized by the contrasting presence of tropical rainforest, tropical monsoon and tropical savanna climates. Convective phenomena are numerous and sometimes still poorly taken into account in climate models, making climate prediction more complex. However, the models agree on a trend towards global warming and an increase in extreme phenomena (excess rainfall and temperature, lack or scarcity of rainfall, etc.) whose consequences on hydrological regimes are sometimes unpredictable.
The impact of climate change on water resources depends not only on changes in the volume, timing, and quality of streamflow and recharge but also on system characteristics, changing pressures on the system, how the management of the system evolves, and what adaptations to climate change are implemented. Non-climatic changes may also have a greater impact on water resources than climate change, as it is mentioned in the Panta Rhei scientific decade 2013–2022 of IAHS, about changes in hydrology and society.
For example, since the 1970s, most of tropical Africa has been experiencing a decline in rainfall, with high evaporation due to the increasing temperature that became more pronounced in the early 1980s, with the repercussion of a decrease in water resources. However, since the 1990s, there has been a slight recovery in rainfall, which is still lower than that recorded in the 1950s in this environment of high evaporative demand. All this, combined with the degradation of the vegetation cover and the reduction in the number of rainy days (concentration of rainfall over short periods), leads to a heavy surface runoff in Sahelian areas and thus to the degradation of ecosystems. Paradoxically also in some tropical humid areas, flood peaks increased while average rainfall and groundwater resources did not. Those changes in precipitation and temperature, as well as non-linear effects on moisture, evapotranspiration and soil, have consequences on the quantity and quality of water resources, agriculture, fisheries and livestock.
Research related to the assessment of past and future climate change, as well as observed changes in hydrological regimes and/or watershed uses, are welcome in this session, including studies about actual and future assessment of evaporation and land-use/cover change interactions with surface runoff conditions.