Abstract
Droughts are a recurrent phenomenon in water abundant tropical countries
worldwide and are expected to become more frequent in the future.
However, drought risk in tropical catchments is poorly understood and
usually not adequately incorporated in water management strategies.
Thus, methodologies to evaluate spatial and seasonal drought risk in
data scarce tropical catchments are urgently needed. We combined hazard
and vulnerability related information to assess drought risk in the test
basin, the rural Muriaé basin in southeast tropical Brazil. Hazard
indicates the cumulative frequency of drought anomalies, while
vulnerability represents the potential of a drought to cause damages in
the socioeconomic system. We simulated subcatchment discharges with a
hydrological model (SWAT) to evaluate spatially distributed hydrological
drought hazard and combined this information with precipitation and
vegetation based indices to define the cumulative frequency of drought
occurrence for each grid cell (0.1°). We tested the sensitivity of
different climate and catchment related model input variables against
low flow events and simulated artificial drought risk scenarios. To
assess vulnerability, we reclassified and weighted globally and
regionally available gridded socioeconomic data. Vulnerability in the
downstream area was found to be stronger which coincided with a higher
hydrological and vegetation based hazard. The drought risk map clearly
identified the downstream area of the Muriaé basin as being exposed to a
stronger drought risk compared to the upstream areas. Only limited
hydrological drought sensitivity of the system against changes in land
cover type and temperature was shown in the model results while geology
and soils turned out to play a larger role for low flows. The drought
scenarios showed that low flows were more severely affected than high
flows by climatic changes such as decreased precipitation. In can be
concluded that our risk assessment methodology offers a holistic,
science based and innovative solution to inform regional planning and
water management institutions dealing with the control of drought
disasters in tropical rural areas. Such drought risk evaluation
frameworks and spatial information are urgently needed in tropical
regions worldwide.