Gustavo Naumann

Monitoring Drought Conditions and Their Uncertainties in Africa Using TRMM Data

AbstractThe main objective of this study is to evaluate the uncertainties due to sample size associated with the estimation of the standardized precipitation index (SPI) and their impact on the level of confidence in drought monitoring in Africa using high-spatial-resolution data from short time series. To do this, two different rainfall datasets, each available on a monthly basis, were analyzed over four river basins in Africa—Oum er-Rbia, Limpopo, Niger, and eastern Nile—as well as at the continental level. The two precipitation datasets used were the Tropical Rainfall Measuring Mission (TRMM) satellite monthly rainfall product 3B43 and the Global Precipitation Climatology Centre full-reanalysis gridded precipitation dataset. A nonparametric resampling bootstrap approach was used to compute the confidence bands associated with the SPI estimation, which are essential for making a qualified assessment of drought events. The comparative analysis of different datasets suggests that for reliable drought moni...

An Optimized System for the Classification of Meteorological Drought Intensity with Applications in Drought Frequency Analysis

AbstractThe adequacy of meteorological drought intensity threshold levels based on deviations of monthly precipitation totals from normal climatological conditions is reconsidered. The motivation for this study is the observation that reference classification systems are fixed for all climatological regions, and threshold levels have been proposed without regard for the statistical distribution of accumulated precipitation in space and time. This misrepresentation of precipitation variability may lead to erroneous estimates of meteorological drought onset in specific areas where natural breaks in the cumulative distribution of monthly precipitation do not fit the generalized classification systems. In this study, a new optimized classification system based on the nonparametric “Fisher–Jenks” algorithm is proposed for the estimation of meteorological drought intensity threshold levels from monthly precipitation totals. The optimized classification system is compared using the tabular accuracy index (TAI) t...

Joint Diagnostic of the Surface Air Temperature in Southern South America and the Madden–Julian Oscillation

Abstract The objective of this research is to explore the relationship between maximum and minimum temperatures, daily precipitation, and the Madden–Julian oscillation (MJO). It was found that the different phases of the MJO show a consistent signal on winter temperature variability and precipitation in southeastern South America. Additionally, this paper explores the spatial–temporal variations of mutual information and joint entropy between temperature and the MJO. A defined spatial pattern was observed with an increased signal in northeastern Argentina and southern Brazil. In the local mutual information analysis, periods in which the mutual information doubled the average values were observed over the entire region. These results indicate that these connections can be used to forecast winter temperatures with a better skill score in situations where both variables covary.

Assessment of drought damages and their uncertainties in Europe

Drought is a natural hazard triggered by a lack of precipitation that can last for several months or years. Droughts can affect a wide range of socio-economic sectors while the related direct and indirect impacts are often difficult to quantify. In this context, drought damage refers to the total or partial destruction of physical assets in the affected area. The main constraint in constructing a robust relationship between the severity of drought events and related damages is the lack of sufficient quantitative impact data. In this paper we propose the use of power-law damage functions to assess the relationship between drought severity and related damages in two economic sectors, namely cereal crop production and hydropower generation, across 21 European countries. The different shapes of the resulting damage functions can be explained by the specific drought vulnerability or adaptive capacity of each sector and country. Due to the scarcity of impact data linked to extreme climate events a bootstrap resampling was performed to assess the potential uncertainties associated with the sample size. This approach helps communicating potential drought impacts and related uncertainties to end users and policy makers in support to the development of drought management plans and long-term adaptation measures.

A Study of Intraseasonal Temperature Variability in Southeastern South America

AbstractThe main goal of this work was to conduct an intraseasonal climate variability analysis using wavelet and principal component analysis over a southeastern South American daily maximum and minimum temperature series from the end of the nineteenth until the beginning of the twenty-first century. The analysis showed that there is a definite and coherent signal in the intraseasonal maximum and minimum temperatures. The most noticeable signal was observed during the winter months. The frequency of the intraseasonal signal was more complex for the maximum temperature, and in some stations, it displayed a bimodal distribution. A defined pattern that described a coherent variability between 30 and 60 days throughout the entire region was observed. This pattern potentially allows classification of the regional variability and adjustments to the temperature forecasting models on a daily basis.

Global Changes in Drought Conditions Under Different Levels of Warming

Higher evaporative demands and more frequent and persistent dry spells associated with rising temperatures suggest that drought conditions could worsen in many regions of the world. In this study, we assess how drought conditions may develop across the globe for 1.5, 2, and 3°C warming compared to preindustrial temperatures. Results show that two thirds of global population will experience a progressive increase in drought conditions with warming. For drying areas, drought durations are projected to rise at rapidly increasing rates with warming, averaged globally from 2.0 month/°C below 1.5°C to 4.2 month/°C when approaching 3°C. Drought magnitudes could double for 30% of global landmass under stringent mitigation. If contemporary warming rates continue, water supply-demand deficits could become fivefold in size for most of Africa, Australia, southern Europe, southern and central states of the United States, Central America, the Caribbean, north-west China, and parts of Southern America. In approximately 20% of the global land surface, drought magnitude will halve with warming of 1.5°C and higher levels, mainly most land areas north of latitude 55°N, but also parts of South America and Eastern and South-eastern Asia. A progressive and significant increase in frequency of droughts is projected with warming in the Mediterranean basin, most of Africa, West and Southern Asia, Central America, and Oceania, where droughts are projected to happen 5 to 10 times more frequent even under ambitious mitigation targets and current 100-year events could occur every two to five years under 3°C of warming. Plain Language Summary This research investigates the climatology of global drought conditions under different global warming levels. We consider warming levels of 1.5 and 2°C set out as mitigation targets in the Paris Agreement, as well as 3°C that is closer to what is expected by the end of the 21st century if current emission trends are retained. We found that the magnitude of droughts is likely to double in 30% of the global landmass under stringent mitigation policies. If global warming continues at the present rate, water supply-demand deficits would increase fivefold while current 1-in-100-year droughts would occur every two to five years for most of Africa, Australia, southern Europe, southern and central United States, Central America, the Caribbean, north-west China, and parts of Southern America. Approximately two thirds of the global population will experience a progressive increase in drought hazard with warming. In drying areas, drought durations are projected to rise rapidly with warming. The main impacts of long-lasting droughts are linked to the lowering of the groundwater and of the water levels in reservoirs. This will impede replenishment of water supplies andmay result in a difficult recovery and prolonged socio-economic impacts after severe droughts.

Global projections of drought hazard in a warming climate: a prime for disaster risk management

Projections of drought hazard (dH) changes have been mapped from five bias-corrected climate models and analyzed at the global level under three representative concentration pathways (RCPs). The motivation for this study is the observation that drought risk is increasing globally and the effective regulation of prevention and adaptation measures depends on dH magnitude and its distribution for the future. Based on the Weighted Anomaly of Standardized Precipitation index, dH changes have been assessed for mid-(2021–2050) and late-century (2071–2099). With a few exceptions, results show a likely increase in global dH between the historical years (1971–2000) and both future time periods under all RCPs. Notwithstanding this worsening trend, it was found that projections of dH changes for most regions are neither robust nor significant in the near-future. By the end of the century, greater increases are projected for RCPs describing stronger radiative forcing. Under RCP8.5, statistically significant dH changes emerge for global Mediterranean ecosystems and the Amazon region, which are identified as possible hotspots for future water security issues. Taken together, projections of dH changes point towards two dilemmas: (1) in the near-term, stake-holders are left worrying about projected increasing dH over large regions, but lack of actionable model agreement to take effective decisions related to local prevention and adaptation initiatives; (2) in the long-term, models demonstrate remarkable agreement, but stake-holders lack actionable knowledge to manage potential impacts far distant from actual human-dominated environments. We conclude that the major challenge for risk management is not to adapt human populations or their activities to dH changes, but to progress on global initiatives that mitigate their impacts in the whole carbon cycle by late-century.

Predictability of the European heat and cold waves

Heat and cold waves may have considerable human and economic impacts in Europe. Recent events, like the heat waves observed in France in 2003 and Russia in 2010, illustrated the major consequences to be expected. Reliable Early Warning Systems for extreme temperatures would, therefore, be of high value for decision makers. However, they require a clear definition and robust forecasts of these events. This study analyzes the predictability of heat and cold waves over Europe, defined as at least three consecutive days of

Estabilidad de la estimación de la onda anual en escala diaria de la temperatura

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