Identifying MAJOR Drought Areas Around The Globe Using New Soil Moisture Observational Process
Introduction: Recent research published in the American Meteorological Society “Journal of Climate” provides an easy and quick methodology to identify where serious drought has developed and is likely to continue (unless a dramatic climate pattern change occurs). The research identifies the influence of deep (10-200 CM) soil moisture anomalies caused by long-term climate and the effectiveness of that deep layer soil moisture deficit on the shallow (0-10 CM) soil moisture anomalies caused by short-term climate and weather phenomena.
Where shallow soil moisture deficit regimes are developing due to short-term dry patterns over regions of deep layer soil moisture shortages serious drought will develop. Climate Impact Company has observed that this combination of circumstances is very likely to strengthen and expand during the warm season as largescale wet synoptic weather patterns easing drought risk are more difficult to generate. Generally, only remains of inland moving tropical (or subtropical) events can reverse the drought conditions produced using the deep/shallow layer soil moisture combination to identify major drought and predict its intensification. Suggested is the increased incidence of flash drought occurring in the climate change era is driven by the deep/shallow layer soil moisture combination described.
The influence of long-term (ranging from several months to years) precipitation patterns on soil moisture is most effectively measured by deep layer soil moisture anomalies while short-term weather and climate precipitation patterns and their influence on soil moisture is best monitored by looking at shallow soil moisture anomalies. Combining the two sets of regimes identifies where harsh drought is occurring (or about to develop) and especially during the warm season raises concern about strengthening and spreading. The most recent research identifying this important process was identified by Sanjiv Kumar, a professor of in the School of Forestry and Wildlife Sciences at Auburn University. The collaborative research included Kumar’s work at Auburn along with Matt Newman of the Boulder, Colorado-based NOAA Earth System Research Laboratory (ESRL) and Yan Wang and Ben Livneh, also at the University of Colorado/Boulder.
Discussion: Using the process identified by Kumar, Newman, Wang and Livneh let’s take a look around the world at where important drought areas is located using the defined methodology.
In the U.S. the short-term climate pattern has produced extreme soil moisture deficit across the 4-Corners region, Texas and the Southeast to Mid-Atlantic U.S. (Fig. 1). The long-term climate has caused deep layer soil moisture deficits most extreme in northeast Mexico and the Southeast U.S. (Fig. 2). Combining the two regimes identifies most of the Gulf of Mexico States (except southeast Texas and Florida peninsula) to the Mid-Atlantic region as a major drought area. Historically, this region encounters wet climate during the cold season if El Nino is present. ENSO forecasts reveal neutral phase of ENSO through quarter 1 of 2020. There is potential for this drought area to worsen and expand prior to the 2020 warm season.
Fig. 1-2: Combining shallow/deep layer soil moisture anomalies to predict a major drought area across North America. Soil moisture data provided by NOAA/ESRL.
South American soil moisture data can vary (widely). However, using the NOAA/ESRL shallow/deep layer soil moisture anomalies (Fig. 3-4) for September 2019 reveals the most likely major drought area as summertime approaches is located across central Brazil. Neutral ENSO forecasts indicate there is potential for this drought area to expand during summertime.
Fig. 3-4: Combing shallow/deep layer soil moisture anomalies to predict a major drought area across South America. Soil moisture data provided by NOAA/ESRL.
El Nino is conventionally known as the climate regime bringing greatest risk of drought to Australia. Weak El Nino 2018-19 has ended although was a likely contributor to deep layer soil moisture deficits in eastern Australia. A lesser-known drought producer is the influence of positive phase Indian Ocean Dipole (+IOD) which is the cause of the widespread shallow soil moisture deficits. The Australian Bureau of Meteorology is forecasting +IOD to continue through the end of 2019. Therefore intense drought already present in western and eastern portions (Fig. 5) of Australia should intensify and expand (Fig. 6). Drought expansion beyond the areas identified could easily occur during quarter 4 of 2019. Australia faxes major drought ahead of their summertime.
Fig. 5-6: Combing shallow/deep layer soil moisture anomalies to predict a major drought area across Australia. Soil moisture data provided by NOAA/ESRL.
A semi-permanent warm and dry upper level ridge pattern centered over Ukraine and Southwest Russia lead to both shallow and deep layer soil moisture deficits (Fig. 7-8) and major drought this past summer and early autumn. The climate pattern described is related to a common summertime upper air pattern across Europe/Western Russia in recent years attributed to the North Atlantic Warming Hole (NAWH). The summer of 2019 pattern produced drought in France but the concentrated area of dryness was across Southwest Russia to Ukraine.
Fig. 7-8: Combing shallow/deep layer soil moisture anomalies to predict a major drought area across Europe/Western Russia. Soil moisture data provided by NOAA/ESRL.
Harsh drought conditions are located across Central and Northeast Russia, eastern portions of China and parts of Indonesia (Fig. 9-10). The NAWH and IOD climate patterns previously described are contributors to the drought.
Fig. 9-10: Combing shallow/deep layer soil moisture anomalies to predict a major drought area across Asia. Soil moisture data provided by NOAA/ESRL.
Shallow and deep layer soil moisture deficits combine to identify major drought in south-central tropical Africa (Fig. 11-12).
Fig. 11-12: Combing shallow/deep layer soil moisture anomalies to predict a major drought area across Africa. Soil moisture data provided by NOAA/ESRL.
Summary: Provided is the combination of September 2019 shallow and deep layer soil moisture anomalies to best ascertain where major drought regions are located (and likely to continue unless a major climate pattern change occurs). The methodology used is produced by recent published research lead by Auburn University and ESRL climate scientists. Identified is the importance of knowing the long-term climate influence on soil moisture best measured using deep layer soil moisture anomalies COMBINED with shallow soil moisture anomalies generally caused by short-term weather regimes. Regarding drought…areas developing shallow soil moisture deficits due to recent weather regimes/events are more likely to transition into drought if the deep layer is also dry. Flash drought also occurs with this condition. Conversely, although not discussed in this document areas of excessive wet shallow soil are more likely to cause flash flooding if the deep layer is also wet.