Abstract
The overarching goal of this work is to develop and demonstrate methods that support effective agro-pastoral risk management in a changing climate. Disaster mitigation strategies, such as the Sendai Framework for Disaster Risk Reduction (SFDRR), emphasize the need to address underlying causes of disaster risk and to prevent the emergence of new risks. Such assessments can be difficult, because they require transforming changes in meteorological outcomes into sector-specific impact. While it is common to examine trends in seasonal precipitation and precipitation extremes, it is much less common to study how these trends interact with crop and pasture water needs. Here, we show that the Water Requirement (WR) component of the widely used Water Requirement Satisfaction Index (WRSI) can be used to enhance the interpretation of precipitation changes. The WR helps answer a key question: was the amount of rainfall received in a given season enough to satisfy a crop or pasture's water needs? Our first results section focuses on analyzing spatial patterns of climate change. We show how WR values can be used to translate east African rainfall declines into estimates of crop and rangeland water deficits. We also show that increases in WR, during recent droughts, has intensified aridity in arid regions. In addition, using the PWB, we also show that precipitation increases in humid areas of western east Africa have been producing increasingly frequent excessive rainfall seasons. The second portion of our paper focuses on assessing temporal outcomes for a fixed location (Kenya) to support drought-management scenario development. Kenyan rainfall is decreasing and population is increasing. How can we translate this data into actionable information? The United Nations and World Meteorological Organization advise nations to proactively plan for agro-hydrologic shocks by setting aside sufficient grain and financial resources to help buffer inevitable low-crop production years. We show how precipitation, WR, crop statistics, and population data can be used to help guide 1-in-10 and 1-in-25-year low crop yield scenarios, which could be used to guide Kenya's drought management planning and development. The first and second research components share a common objective: using the PWB to translate rainfall data into more actionable information that can inform disaster risk management and development planning.
Highlights
AND RATIONALEIn this study, we introduce a new Plant Water Balance (PWB) metric and demonstrate how it can be used to support trend analyses and risk management in east Africa (0–18◦N, 20◦E−51◦E)
We show how Water Requirements (WR) values can be used to translate east African rainfall declines into estimates of crop and rangeland water deficits
The core of the PWB is a comparison of the amount of water supply and plant water demand accumulated over the growing season, from the first dekad associated with Start of Season (SOS) through to the end of season at a dekad corresponding to SOS+Length of Growing Period (LGP)
Summary
AND RATIONALEIn this study, we introduce a new Plant Water Balance (PWB) metric and demonstrate how it can be used to support trend analyses and risk management in east Africa (0–18◦N, 20◦E−51◦E). Beginning in 2005 (Funk et al, 2005) and continuing to the present (Gebrechorkos et al, 2019), many studies have documented the decline in the eastern east Africa (east Africa east of 38◦E and south of 8◦N) boreal spring “Long” rains. While it is generally accepted that this decline is associated with an intensification of the Indian Ocean branch of the Walker Circulation, as suggested in 2008 (Funk et al, 2008), the primary driver of that intensification is likely due to changes in the Pacific, and not Indian, Ocean (Williams and Funk, 2011; Lyon and DeWitt, 2012) These changes involve a combination of humaninduced warming in the western Pacific and natural, La Niña-like, cool sea surface temperatures in the equatorial eastern Pacific (Hoell and Funk, 2013a,b; Liebmann et al, 2014). One study (Wainwright et al, 2019) suggested that the recent decline is strongly associated with a shorter rainy season, with warmer waters to the south of east Africa delaying the onset and decreasing surface pressures over Arabia, supporting an earlier cessation of the rainy season
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