Remote sensing assessment of available green water to increase crop production in seasonal floodplain wetlands of sub-Saharan Africa

Producing more food for a growing population requires sustainable crop intensification and diversification, particularly in high-potential areas such as the seasonal floodplain wetlands of sub-Saharan Africa (SSA). With emerging water shortages and concerns for conserving these multi-functional wetlands, a further expansion of the cropland area must be avoided as it would entail increased use of blue water for irrigation and infringe on valuable protected areas. We advocate an efficient use of the prevailing green water on the existing cropland areas, where small-scale farmers grow a single crop of rainfed lowland rice during the wet season. However, soil moisture at the onset of the rains (pre-rice niche) and residual soil moisture after rice harvest (post-rice niche) may suffice to cultivate short-cycled crops. We developed a methodological approach to analyze the potential for green water cultivation in the pre- and post-rice niches in the Kilombero Valley Floodplain in Tanzania, as a representative case for seasonal floodplain wetlands in SSA. The three-step approach used open-access remote sensing datasets to: (i) extract cropland areas; (ii) analyze soil moisture conditions using evaporative stress indices to identify the pre- and post-rice niches; and (iii) quantify the green water availability in the identified niches through actual evapotranspiration (AET).