US: Rain gauges are few and far between in the Amazon Basin, which makes measuring rainfall and monitoring drought a difficult task. Satellite precipitation data helps to fill the gap, but high-resolution satellite records do not cover a very long time period. Now, for the first time, scientists have been able to address this problem by combining different satellite records to make a global long-term and near real-time precipitation record.
Global high-resolution satellite records of rainfall only go back a decade or so – not long enough to monitor the comings and goings of droughts. However, there is a 30-year low-resolution satellite-based precipitation data set known as the Global Precipitation Climatology Project (GPCP). But GPCP has a time lag of around 12 to 18 months – not much help if you need to monitor droughts in real time.
To overcome these problems and create a global long-term and near real-time satellite record of rainfall, Amir AghaKouchak and Navid Nakhjiri from the University of California Irvine, US, combined these two very different satellite records using a Bayesian correction.
“In statistics and probability theory, the Bayesian approach provides a way to update or correct an existing prediction given new or additional information, data, or evidence,” explained AghaKouchak. “Here we correct the near real-time satellite data with historical observations from long-term satellite observations. In other words, using the overlap between the two data sets, we estimate the likely correct value of near real-time satellite data.”
In recent years, regional and global climate models have been used extensively to study droughts and their causes. The new record is observation-driven and model-independent, so can be used to validate and verify models.
Already the new record has correctly identified several recent major events such as the 2011 Texas, 2010 Amazon and 2010 Horn of Africa droughts. AghaKouchak and Nakhjiri are confident that this combined satellite record will help to identify and monitor future droughts. “Since near real-time satellite observations are available within a few hours to days, one can monitor droughts across the globe in a timely manner,” said AghaKouchak. “This product is particularly useful for remote regions and basins with few rain gauges.”
In fact the researchers have already used the new record to identify areas that show a significant increase in drought frequency and they hope to publish these findings soon.
Source: Environmental Research