Detecting droughts and floods in the Greater Horn of Africa with satellite gravity and precipitation and or soil moisture
In recent years, the Greater Horn of Africa has suffered from prolonged droughts, associated with forced migration and food and water security issues. The recent droughts then came to an abrupt ending with a period of excessive rainfall and flash floods in Nov-Dec 2023.
These extreme events fall in line with the general expectation of an intensifying water cycle, and concerns can be raised to what extent the region is resilient to such extremes.
Drought indicators are a way to study these events and can reduce the complexity of datasets in more accessible numeric values of drought intensity.
Satellite gravimetry, as applied in the GRACE (Gravity Recovery and Climate Experiment) and GRACE-Follow on mission, can detect changes in the gravity field induced by water mass transport. These gravity observations are therefore influenced by droughts and floods and have been recently used to construct drought indicators.
A disadvantage of GRACE is the low spatial resolution, so an opportunity arises to create a multi-variate drought index based on GRACE data and other variables such as precipitation or soil moisture. The latter datasets generally have better spatial resolution to inform the higher spatial details.
In this topic, you will generate and investigate the suitability of a multi-variate drought index, and its potential use in the Greater Horn of Africa.
One way to construct a multi-variate drought indicator is to link individual indicators/variables into joint probabilities through a Copula function (e.g. Hoa et al. 2013).
The suitability of the drought indicators will be tested by comparison with other known indicators and the ability to pick up the recent (2021-2023) drought and flooding episodes.
Besides GRACE and GRACE-FO data, soil moisture and or precipitation data can be sourced from satellite products such as the CCI Soil moisture product or Chirps data.
- Gerdener, H., Engels, O., Kusche, J., 2020. A framework for deriving drought indicators from the Gravity Recovery and Climate Experiment (GRACE). Hydrology and Earth System Sciences 24, 227–248. https://doi.org/10.5194/hess-24-227-2020
- Hao, Z., AghaKouchak, A., 2013. Multivariate Standardized Drought Index: A parametric multi-index model. Advances in Water Resources 57, 12–18. https://doi.org/10.1016/j.advwatres.2013.03.009
The intensifying water cycle is a tough wicked problem to cope with as crops are exposed to more harsh conditions, and current (farming and water management) practices may be vulnerable to water cycle intensification. A drought indicator can help to inform planning but also can potentially be used in efficiently allocating and concentrating resources to those areas which are mostly in need.
This topic can therefore be adapted for spatial engineering by considering the need for a (better) drought indicator from the demand side. Relevant questions which can be asked is how and where there is added value of (improved) drought indicators for stakeholders in the region.