Assessment of seasonal soil moisture forecasts over Southern South America with emphasis on dry and wet events

SPENNEMANN, PABLO C.; RIVERA, JUAN A.; OSMAN, MARISOL; SAULO, A. CELESTE; PENALBA, OLGA C.

JOURNAL OF HYDROMETEOROLOGY

AMER METEOROLOGICAL SOC

Año: 2017

1525-755X

The importance of forecasting extreme wet and dry conditions from weeks to months in advance relies on the need to prevent considerable socio-economic losses, mainly in regions of large populations and where agriculture is a key value for the economies, such as Southern South America (SSA). To improve the understanding of the performance and uncertainties of seasonal soil moisture and precipitation forecasts over SSA, this study aims to: 1) perform a general assessment of the Climate Forecast System version-2 (CFSv2) soil moisture and precipitation forecasts against observations and soil moisture simulations based on GLDAS-2.0; 2) evaluate the CFSv2?s ability to represent wet and dry events through forecasted Standardized Precipitation Index (SPI) and the Standardized Soil Moisture Anomalies (SSMA); and 3) analyze the capability of a statistical methodology (merging observations and forecasts) in representing a severe drought event.Results show that both SPI and SSMA forecast skill is regionally and seasonally dependent. In general a fast degradation of the forecasts skill is observed as the lead time increases, resulting in almost no added value with regard to climatology at lead times longer than 3 months. Additionally, a better performance of the SSMA forecasts is observed compared to the SPI3, with a higher skill for dry events against wet events. The CFSv2 forecasts are able to represent the spatial patterns of the 2008-2009 severe drought event, although it shows crucial limitations regarding to the identification of drought onset, duration, severity and demise, considering both meteorological (SPI) and agricultural (SSMA) drought conditions.