Drought risk assessment in Mediterranean agricultural watersheds: A case study in Central Italy
Graphical Abstract
Introduction
The occurrence and severity of droughts - defined as “periods of abnormally dry weather long enough to cause a serious hydrological imbalance” (IPCC, 2012) – are expected to increase in the future due to climate change (Dai, 2011; IPCC, 2022). The Italian peninsula, located in the heart of the Mediterranean region, will be a hotspot for climate change (MedECC, 2020, Spano et al., 2020, Zollo et al., 2016), facing more frequent and intense drought events (Cammalleri et al., 2020, Caporali et al., 2021, Castellari et al., 2014, OECD, 2021). Droughts, characterized in terms of frequency, severity, duration, and extent, have typically been considered a natural phenomenon triggered by lack of precipitation, (Zargar et al., 2011). Different types of droughts have been identified, including (a) the meteorological drought – “a lack of precipitation over a region for a period of time”, (b) the agricultural drought – “a period with declining soil moisture and consequent crop failure”, (c) the hydrological drought – “a period with inadequate surface and subsurface water resources for established water uses”, and (d) the socioeconomic drought –“a failure of water resources systems to meet water demands” (Mishra and Singh, 2010). In the past, droughts were considered to propagate from meteorological to agricultural, hydrological and socioeconomic droughts. This approach has been recently questioned for its over-simplification since it fails to account for (i) feedback and trade-offs between social and physical processes, (ii) direct effects of human-induced climate change and (iii) long-term environmental impacts of drought (AghaKouchak et al., 2021, Crausbay et al., 2017, Di Baldassarre et al., 2021, Van Loon et al., 2016). As a result, the terms “ecological drought” and “human-induced hydrological drought” were recently introduced (Crausbay et al., 2017, Van Loon et al., 2016). A further step will need to be done to improve our understanding of “anthropogenic drought”, a multidimensional and multiscale phenomenon that should be intended as a “process” rather than a “product” (AghaKouchak et al., 2021).
Globally, it is estimated that drought damages account for a fifth of the total damages caused by natural hazards (World Meteorological Organization (WMO) and Global Water Partnership (GWP), 2017). In Europe, the annual economic losses caused by droughts are estimated to be around € 9 billion (€ 1.4 billion for Italy), mostly related to the agricultural sector (Cammalleri et al., 2020), with significant spatial variability between different regions (García-León et al., 2021). The entity of the losses, along with the expected increase due to climate change, boosted the interest of researchers and decision-makers in this topic (Hagenlocher et al., 2019). To better deal with droughts, recent studies call for a shift from the so-called “reactive” approach, taken in emergency situations and considered technically and economically inefficient, towards a “proactive” approach, including appropriate measures developed with the involvement of multiple stakeholders (Carrão et al., 2016, Murthy et al., 2015, Vogt et al., 2018). In fact, preparation and mitigation costs are by far lower compared to the relief costs, which significantly surge in case of inaction (Vogt et al., 2018; World Meteorological Organization (WMO) and Global Water Partnership (GWP), 2017). To better prepare for droughts, vulnerability and risk assessments are considered of major importance for developing sound and effective strategies (World Meteorological Organization (WMO) and Global Water Partnership (GWP), 2014; World Bank, 2019).
Commonly, drought hazard is quantified by indicators of drought severity, frequency, intensity, and duration. Many drought hazard indicators exist to describe meteorological, agricultural, and hydrological droughts (Kchouk et al., 2022, Mishra and Singh, 2010, Zargar et al., 2011), which might refer directly to physical variables such as precipitation, evapotranspiration, soil moisture or streamflow, or can infer drought from vegetation health. Despite the availability of multiple hazard indicators, drought risk assessments are generally carried out with the use of one or a few hazard indicators. However, considering hazard indicators of meteorological, agricultural, and hydrological droughts can better embrace the complexity of drought hazards (Sun et al., 2012, World Bank, 2019). Furthermore, the most common approach to represent drought hazard is by using historical data; nevertheless, many authors (e.g. Hagenlocher et al., 2019; Vogt et al., 2018) claim the importance of including predictions of future droughts, but at the cost of higher uncertainty (Mysiak et al., 2018).
Two major limitations to the validity and practical use of drought risk assessments are commonly shared: (1) only 11% of them conduct some form of validation and, (2) they generally miss a link with possible adaptation strategies (Hagenlocher et al., 2019). The robustness of the methodology applied can be evaluated with uncertainty or sensitivity analyses (OECD, 2008), sometimes referred to as internal validation (Carrão et al., 2016, Fontaine and Steinemann, 2009), or by comparing results with external information, referred to also as external validation. Finding suitable data for external validation might be impossible in some regions of the world and when dealing with small scales. Additionally, the validation with external datasets is complicated by the fact that composite indicators aim to represent complex past and future dynamics. Hence, the validity of composite indicators is generally evaluated by performing uncertainty and sensitivity analyses (OECD, 2008). Even if examples exist, a shared, simple but at the same time robust methodology for internal validation is still missing.
The main objective of this study is to propose a detailed and integrated drought risk assessment of Mediterranean agricultural systems and present an application to the municipalities located in coastal watersheds of Central and Southern Tuscany (Central Italy). These areas are susceptible to drought especially during the summer months, due to the concurrent high water demands for domestic and agricultural uses. Key innovations introduced in this paper are (1) a complete robustness evaluation of the assessment by applying alternative methodologies in crucial steps of the drought risk assessment; (2) the use of archetype analysis to streamline the identification of exposure and vulnerability patterns and propose a link with possible adaptation strategies.
Section snippets
Methodology
The methodology of this study draws on the guidelines introduced by OECD (2008) and the approaches of other drought risk assessments (Hagenlocher et al., 2018, Meza et al., 2020), with the addition of a robustness evaluation and archetype analysis for a more integrated assessment. The eight operational steps are:
- 1)
Conceptual framework definition;
- 2)
Study area definition;
- 3)
Identification of indicators;
- 4)
Data acquisition and pre-processing;
- 5)
Multicollinearity analysis;
- 6)
Normalization and weighted aggregation;
- 7)
Multicollinearity analysis
Several significant multicollinearities were detected (p-value<0.05). As a result, the indicator “Share of horticulture and fruticulture” was excluded from exposure indicators since it was highly correlated with “Value of Agricultural Products” and “Volume of water used for irrigation”. For the vulnerability indicators, “Climate interference” and “Water deficit” were excluded since their variability was explained by other indicators, namely “Soil erosion” and “Soil fertility”. Similarly, “Share
Past and future drought hazard
Interesting results were found in the estimation of drought hazard. Correlations between the total severity, duration, and frequency calculated with SPI3, SPI6, SPI12, and VHI in the 58 municipalities are poor, implying that the use of only one of them would have resulted in a different pattern of drought hazard. The non-standardized indicators of future hazard showed very high correlations when considering the same indicator in the short-, medium-, and long-term future, while much worse
Conclusion
A complete drought risk assessment was conducted for 58 municipalities belonging to five coastal watersheds in Tuscany (Central Italy). The proposed approach allowed to produce a policy-relevant drought risk assessment, even though adjustments could further improve the methodology. The inclusion of multiple drought hazard indicators provided a more comprehensive analysis of drought risk. The use of future projections to account for climate change impacts also confirmed the patterns of past
Funding
This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.
Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
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