Exploring the link between drought indicators and impacts

Abstract

Abstract. Current drought monitoring and early warning systems use different indicators for monitoring drought conditions and apply different indicator thresholds and rules for assigning drought intensity classes or issue warnings or alerts. Nevertheless, there is little knowledge on the meaning of different hydro-meteorologic indicators for impact occurrence on the ground. To date, there have been very few attempts to systematically characterize the indicator-impact relationship owing to sparse and patchy data on drought impacts. The newly established European Drought Impact report Inventory (EDII) offers the possibility to investigate this linkage. The aim of this study was to explore the link between hydro-meteorologic indicators and drought impacts for the case study area Germany and thus to test the potential of qualitative impact data for evaluating the performance of drought indicators. As drought indicators two climatological drought indices -the Standardized Precipitation Index (SPI) and the Standardized Precipitation Evapotranspiration Index (SPEI) -as well as streamflow and groundwater level percentiles were selected. Linkage was assessed though data visualization, extraction of indicator values concurrent with impact onset, and correlation analysis between monthly time series of indicator and impact data at the federal state level, and between spatial patterns for selected drought events. The analysis clearly revealed a significant moderate to strong correlation for some states and drought events allowing for an intercomparison of the performance of different drought indicators. Important findings were strongest correlation for intermediate accumulation periods of SPI and SPEI, a slightly better performance of SPEI versus SPI, and a similar performance of streamflow percentiles to SPI in many cases. Apart from these commonalities, the analysis also exposed differences among federal states and drought events, suggesting that the linkage is time variant and region specific to some degree. Concerning "thresholds" for drought impact onset, i.e. indicator values concurrent with past impact onsets, we found that no single "best" threshold value can be identified but impacts occur within a range of indicator values. Nevertheless, the median of the threshold distributions showed differences between northern/northeastern versus southern/southwestern federal states, and among drought events. While the findings strongly depend on data and may change with a growing number of EDII entries in the future, this study clearly demonstrates the feasibility of evaluating hydro-meteorologic variables with text-based impact reports and highlights the value of impact reporting as a tool for monitoring drought conditions.

Multiscale evaluation of the Standardized Precipitation Index as a groundwater drought indicator

“…It is however noted that such analysis would require a good quality of impact variable data sets and, for many regions for which we need reliable and accurate data sets (e.g., on groundwater drought information), these observations are often not readily available. Nevertheless, the issue of analyzing an appropriate drought timescale is not only specific for the groundwater system, but is also relevant for several other hydrological and ecological systems (e.g., Pasho et al, 2010;Vicente-Serrano et al, 2011López-Moreno et al, 2013;VicenteSerrano et al, 2013;Haslinger et al, 2014;Bachmair et al, 2015;Van Loon, 2015). Figure 5 shows the exemplary time series of the SGI and SPI at 6 and 12 months of the accumulation periods for all wells and grid cells and their respective spatial averages for an overlapping period of 1995-2006.…”

“…In recent years there have been some efforts to analyze the relationship between meteorological and groundwater-based drought indices (Bloomfield and Marchant, 2013;Folland et al, 2015;Bachmair et al, 2015). Bloomfield and Marchant (2013), for example, introduced the Standardized Groundwater level Index (SGI), similar to the SPI, and found a site-specific relationship between the two indices.…”

Analysis of hydrological data with correlation matrices: technical implementation and possible applications

“…Indeed, Kingston et al (2015) found that a higher number of European droughts was identified by the SPEI than by the SPI. Likewise, Bachmair et al (2015) found higher correlations for SPEI than for SPI. The findings by Bachmair et al (2015), Stagge et al (2015a) and Blauhut et al (2016) similarly suggest that SPEI tends to be a better predictor of drought impacts than SPI, but a combination of different aggregation periods and indices generally is considered most favorable.…”

“…Likewise, Bachmair et al (2015) found higher correlations for SPEI than for SPI. The findings by Bachmair et al (2015), Stagge et al (2015a) and Blauhut et al (2016) similarly suggest that SPEI tends to be a better predictor of drought impacts than SPI, but a combination of different aggregation periods and indices generally is considered most favorable. In the given case, however, the behavior of the SPEI only minimally deviates from the SPI, as can be seen from the high correlation between the two indices (see Fig.…”

Epistemic uncertainties and natural hazard risk assessment. 1. A review of different natural hazard areas

“…as a result of infrastructure failures, health and psychological impacts) can also be difficult to assess. More geographically explicit damage relationships are needed for hazards such as droughts (Bachmair et al, 2015;Blauhut et al, 2015) or tsunamis (Goda and Song, 2016), which 20 cover potentially large and heterogeneous areas. Potential sources of damage are even more difficult to estimate for future events, as a result of epistemic uncertainties (e.g.…”