Abstract
Abstract. Globally, there have been many extreme weather events in recent decades. A challenge has been to determine whether these extreme weather events have increased in number and intensity compared to the past. This challenge is made more difficult due to the lack of long-term instrumental data, particularly in terms of river discharge, in many regions including Southeast Asia. Thus our main aim in this paper is to develop a river basin scale approach for assessing interannual hydrometeorological and discharge variability on long, palaeological, time scales. For the development of the basin-wide approach, we used the Mekong River basin as a case study area, although the approach is also intended to be applicable to other basins. Firstly, we derived a basin-wide Palmer Drought Severity Index (PDSI) from the Monsoon Asia Drought Atlas (MADA). Secondly, we compared the basin-wide PDSI with measured discharge to validate our approach. Thirdly, we used basin-wide PDSI to analyse the hydrometeorology and discharge of the case study area over the study period of 1300–2005. For the discharge-MADA comparison and hydrometeorological analyses, we used methods such as linear correlations, smoothing, moving window variances, Levene type tests for variances, and wavelet analyses. We found that the developed basin-wide approach based on MADA can be used for assessing long-term average conditions and interannual variability for river basin hydrometeorology and discharge. It provides a tool for studying interannual discharge variability on a palaeological time scale, and therefore the approach contributes to a better understanding of discharge variability during the most recent decades. Our case study revealed that the Mekong has experienced exceptional levels of interannual variability during the post-1950 period, which could not be observed in any other part of the study period. The increased variability was found to be at least partly associated with increased El Niño Southern Oscillation (ENSO) activity.
Highlights
The last decade has been a decade of extreme weather events, with record breaking events being observed in many regions of the world (Coumou and Rahmstorf, 2012)
The findings suggest that the basin averaged Palmer Drought Severity Index (PDSI) derived from Monsoon Asia Drought Atlas (MADA) is a good proxy for climate variability induced by El Nino Southern Oscillation (ENSO), and much of the increased variability of the recent decades is associated with increased ENSO activity (Fig. 4b)
Our aim was to develop an approach based on the Monsoon Asia Drought Atlas (MADA) for examining the recent interannual variability of hydrometeorological conditions and river discharge, at a river basin scale, in the perspective of long-term variability
Summary
The last decade has been a decade of extreme weather events, with record breaking events being observed in many regions of the world (Coumou and Rahmstorf, 2012). The Intergovernmental Panel on Climate Change (IPCC) reports that globally there is evidence that the number of weather and climate extremes, of warm spells or heat waves and heavy precipitation, has increased since 1950, but that large regional differences exist (IPCC, 2012). Due to the limited availability of long-term observed records of climatological and hydrological parameters, a major challenge has been determining whether the frequency or intensity of extreme events have increased (IPCC, 2012). To overcome this deficiency, data periods have been extended by reconstructing past climates with palaeoclimate proxies Data periods have been extended by reconstructing past climates with palaeoclimate proxies (e.g. Dobrovolny et al, 2010; Cook et al, 2007).
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