Assessing precipitation trends in the Americas with historical data: A review. (10th November 2019) - Carvalho, Leila M. V.
Abstract: North, Central, and South America (collectively referred to as the Americas) extend across two hemispheres, and together cover approximately 28% of Earth's land area and are home to about 13% of the world's population. Unique ecosystems, diversified cultures, and communities that inhabit the region rely on precipitation delivered yearly by multiple systems, including mid‐latitudes storms, the North and South American Monsoons, and tropical storms and hurricanes. The rapid warming of the Earth's atmosphere and oceans combined with internal variability of the climate system, have modified precipitation patterns from the tropics to high latitudes. In the Americas, instrumental records have shown evidence of upward trends in extreme precipitation (amount, intensity, and frequency) in many areas. The most consistent evidence of precipitation trends occurs in mid‐latitudes of North America and in the subtropics of South America. Recent studies have indicated a poleward shift of heavy precipitation associated with South American Monsoon. Nonetheless, the deficient network of rain gauges in vast areas over tropical Americas limits the assessment of trends in regions with heavy rainfall amounts. Additionally, observed trends in the North America monsoon precipitation are difficult to separate from the contribution of tropical storms and hurricanes. Furthermore, coupled modes such as the El Nino/Southern Oscillation, the Pacific Decadal Oscillation, and the Atlantic Multidecadal Oscillation modulate precipitation in the Americas, from the tropics to the extratropics, and these teleconnections are relevant to assess precipitation trends using historical records. This review evaluates all these complex issues focusing on observations based on instrumental datasets. This article is categorized under: Paleoclimates and Current Trends > Modern Climate Change Abstract : Count of rain gauge station data in four consecutive 28‐year period that have been utilized in the construction of the monthly precipitation climate data from the University of East Anglia's Climate Research Unit Timeseries (CRU‐TS) at 0.5° × 0.5° spatial resolution (top row). The high variability in the count of stations from 1901 to 2016 is evident in many countries in the Americas. The scarceness and sparseness of stations are most remarkable over tropical South America and high latitudes north of 50°N (Artic) and south of 50°S. The January 99th monthly mean precipitation is calculated for the same period using the CRU‐TS dataset (bottom row). Dramatic changes in the 99th percentile are observed where precipitation is climatologically more intense over tropical South America. These variations are likely artifacts resulting from the spatial and temporal changes of available rain gauges for the calculation of the CRU‐TS gridded precipitation. The availability of rain gauges in the 20th century is among the most challenging issues to assess precipitation trends and their extremes using historical data in most countries in the Americas. CRU‐TS is freely available at http://www.cru.uea.ac.uk/about-cru .