Drought monitoring over the Kruger National Park (2000-2020) integrating remote sensing data.

Semiarid regions shaped as a mosaic of savanna-type rangelands, croplands, and other uses such as livelihoods, or natural reserves, cover large areas in Southern Africa. They constitute an essential example of multiple uses of natural resources, combining a high environmental value with great importance in the rural economy and development. These systems are water-limited and highly sensitive to changes in climate, environmental conditions, and land management practices. Although the vegetation of these areas is adapted to variable climatic conditions and dry periods, the increase in drought intensity, duration, and frequency precipitate their degradation. 

 

In Southern Africa, recurrent droughts have strained rainfed agriculture and pasture production, decimating livestock and wildlife. During 2015 and 2016, South African savannas were subjected to a severe drought associated with a strong El Niño event. Open-source satellite time series provide vital information to assess water availability and long-term drought, to help design early warning and conservation strategies. 

 

In this work, we applied the TSEB (Two Source Energy Balance) model integrating MODIS-derived products (1 km) from 2000 to 2021 over the Kruger National Park (KNP) in South Africa. The model was previously validated over the Skukuza experimental site with good agreement. ET followed precipitation rates, although some years with low precipitation maintained average ET values. This may be caused by the ability of the trees to reach groundwater (deep fractured aquifers and alluvial aquifers can be found in the KNP). During some years (e.g., 2004, 2009), annual total ET was much higher than mean annual values. This may be caused by an extreme annual evaporative atmospheric demand and relatively high precipitation. The anomalies of the ratio of ET to reference ET were used as an indicator of agricultural drought on annual scales, and 2002/2003, 2007/2008 and 2015/2016 years stood out for their negative values. The approach helped to model drought over Kruger Park in the long term, providing an insight into the characteristics of the events.

Acknowledgment: This work has been carried out through the project "DroughT impACt on the vegeTation of South African semIarid mosaiC landscapes: Implications on grass-crop-lands primary production" funded by the European Space Agency in the framework of the "EO AFRICA R&D Facility".