Hydrological drought across the world: impact of climate and physical catchment structure

443

304

Abstract. Since 2010 an uninterrupted sequence of dry years, with annual rainfall deficits ranging from 25 to 45 %, has prevailed in central Chile (western South America, 30-38 • S). Although intense 1-or 2-year droughts are recurrent in this Mediterranean-like region, the ongoing event stands out because of its longevity and large extent. The extraordinary character of the so-called central Chile megadrought (MD) was established against century long historical records and a millennial tree-ring reconstruction of regional precipitation. The largest MD-averaged rainfall relative anomalies occurred in the northern, semi-arid sector of central Chile, but the event was unprecedented to the south of 35 • S. ENSO-neutral conditions have prevailed since 2011 (except for the strong El Niño in 2015), contrasting with La Niña conditions that often accompanied past droughts. The precipitation deficit diminished the Andean snowpack and resulted in amplified declines (up to 90 %) of river flow, reservoir volumes and groundwater levels along central Chile and westernmost Argentina. In some semi-arid basins we found a decrease in the runoff-to-rainfall coefficient. A substantial decrease in vegetation productivity occurred in the shrubland-dominated, northern sector, but a mix of greening and browning patches occurred farther south, where irrigated croplands and exotic forest plantations dominate. The ongoing warming in central Chile, making the MD one of the warmest 6-year periods on record, may have also contributed to such complex vegetation changes by increasing potential evapotranspiration. We also report some of the measures taken by the central government to relieve the MD effects and the public perception of this event. The understanding of the nature and biophysical impacts of the MD helps as a foundation for preparedness efforts to confront a dry, warm future regional climate scenario.

Section: Surface Hydrologysupporting

confidence: 63%

The 2010–2015 megadrought in central Chile: impacts on regional hydroclimate and vegetation

Garreaud

Álvarez-Garretón

Barichivich

et al. 2017

443

304

“…A corresponding accumulation period, shown by the vertical arrow below each of the crosscorrelation curves, can also be identified in these plots. Previous studies of drought propagation have distinguished four components in the propagation of drought: pooling, attenuation, lag and lengthening (Chagnon Jr., 1987;Peters, 2003;Peters et al, 2003;van Loon and van Lanen, 2012;. Here we are interested in understanding the full spectrum of behaviour of lag correlation between SPI and SGI.…”

Section: Correlation Between Sgi and Spimentioning

confidence: 99%

“…A number of studies have sought to develop a better understanding of groundwater droughts in the context of meteorological drivers and, in particular, how droughts propagate through hydrological systems (Eltahir and Yeh, 1999;Peters, 2003;Peters et al, 2003Peters et al, , 2005Peters et al, , 2006Tallaksen et al, 2006Tallaksen et al, , 2009Leblanc et al, 2009;van Lanen et al, 2013). These studies have usually focussed on the catchment scale and have brought process understanding to bear on the evolution of groundwater droughts.…”

Section: Introductionmentioning

confidence: 99%

Analysis of groundwater drought building on the standardised precipitation index approach

Bloomfield

Marchant

2013

338

328

Abstract.A new index for standardising groundwater level time series and characterising groundwater droughts, the Standardised Groundwater level Index (SGI), is described. The SGI builds on the Standardised Precipitation Index (SPI) to account for differences in the form and characteristics of groundwater level and precipitation time series. The SGI is estimated using a non-parametric normal scores transform of groundwater level data for each calendar month. These monthly estimates are then merged to form a continuous index. The SGI has been calculated for 14 relatively long, up to 103 yr, groundwater level hydrographs from a variety of aquifers and compared with SPI for the same sites. The relationship between SGI and SPI is site specific and the SPI accumulation period which leads to the strongest correlation between SGI and SPI, q max , varies between sites. However, there is a consistent positive linear correlation between a measure of the range of significant autocorrelation in the SGI series, m max , and q max across all sites. Given this correlation between SGI m max and SPI q max , and given that periods of low values of SGI can be shown to coincide with previously independently documented droughts, SGI is taken to be a robust and meaningful index of groundwater drought. The maximum length of groundwater droughts defined by SGI is an increasing function of m max , meaning that relatively long groundwater droughts are generally more prevalent at sites where SGI has a relatively long autocorrelation range. Based on correlations between m max , average unsaturated zone thickness and aquifer hydraulic diffusivity, the source of autocorrelation in SGI is inferred to be dependent on dominant aquifer flow and storage characteristics. For fractured aquifers, such as the Cretaceous Chalk, autocorrelation in SGI is inferred to be primarily related to autocorrelation in the recharge time series, while in granular aquifers, such as the Permo-Triassic sandstones, autocorrelation in SGI is inferred to be primarily a function of intrinsic saturated flow and storage properties of aquifer. These results highlight the need to take into account the hydrogeological context of groundwater monitoring sites when designing and interpreting data from groundwater drought monitoring networks.

“…To help develop an optimal monitoring network for groundwater resources under drought conditions, Chang and Teoh (1995) described the heterogeneous response of groundwater levels at 13 observation boreholes to meteorological droughts across a basin in Ohio, USA, although they did not investigate the hydrogeological causes of the heterogeneity. and Van Lanen and Tallaksen (2007) observed that drought characteristics derived from groundwater levels have "spatial effects" and noted that these spatial effects on groundwater drought are an important consideration when monitoring droughts using groundwater levels. Van Lanen and Tallaksen (2007) compared modelled groundwater recharge and discharge for a humid continental climate (Missouri, USA) and a tropical savannah climate (Guinea) for quick-and slow-responding catchments and showed that both climatology and the responsiveness of the catchment as defined by the aquifer characteristics have an influence on drought generation.…”

Section: Controls On Spatial Heterogeneity In Groundwater Droughtmentioning

confidence: 99%

Regional analysis of groundwater droughts using hydrograph classification

Bloomfield

Marchant

Bricker

et al. 2015

112

Abstract. Groundwater drought is a spatially and temporally variable phenomenon. Here we describe the development of a method to regionally analyse and quantify groundwater drought. The method uses a cluster analysis technique (nonhierarchical k-means) to classify standardised groundwater level hydrographs (the standardised groundwater level index, SGI) prior to analysis of their groundwater drought characteristics, and has been tested using 74 groundwater level time series from Lincolnshire, UK. Using the test data set, six clusters of hydrographs have been identified. For each cluster a correlation can be established between the mean SGI and a mean standardised precipitation index (SPI), where each cluster is associated with a different SPI accumulation period. Based on a comparison of SPI time series for each cluster and for the study area as a whole, it is inferred that the clusters are independent of the driving meteorology and are primarily a function of catchment and hydrogeological factors. This inference is supported by the observation that the majority of sites in each cluster are associated with one of the principal aquifers in the study region. The groundwater drought characteristics of the three largest clusters, which constitute ∼ 80 % of the sites, have been analysed. There are differences in the distributions of drought duration, magnitude and intensity of groundwater drought events between the three clusters as a function of autocorrelation of the mean SGI time series for each cluster. In addition, there are differences between the clusters in their response to three major multi-annual droughts that occurred during the analysis period. For example, sites in the cluster with the longest SGI autocorrelation experience the greatest-magnitude droughts and are the slowest to recover from major droughts, with groundwater drought conditions typically persisting at least 6 months longer than at sites in the other clusters. Membership of the clusters is shown to be related to unsaturated zone thickness at individual boreholes. This last observation emphasises the importance of catchment and aquifer characteristics as (non-trivial) controls on groundwater drought hydrographs. The method of analysis is flexible and can be adapted to a wide range of hydrogeological settings while enabling a consistent approach to the quantification of regional differences in response of groundwater to meteorological drought.