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. 2015 Mar 17;112(11):3241-6.
doi: 10.1073/pnas.1421533112. Epub 2015 Mar 2.

Climate change in the Fertile Crescent and implications of the recent Syrian drought

Colin P Kelley  1 , Shahrzad Mohtadi  2 , Mark A Cane  3 , Richard Seager  3 , Yochanan Kushnir  3
Affiliations

Climate change in the Fertile Crescent and implications of the recent Syrian drought

Colin P Kelley et al. Proc Natl Acad Sci U S A. .

Abstract

Before the Syrian uprising that began in 2011, the greater Fertile Crescent experienced the most severe drought in the instrumental record. For Syria, a country marked by poor governance and unsustainable agricultural and environmental policies, the drought had a catalytic effect, contributing to political unrest. We show that the recent decrease in Syrian precipitation is a combination of natural variability and a long-term drying trend, and the unusual severity of the observed drought is here shown to be highly unlikely without this trend. Precipitation changes in Syria are linked to rising mean sea-level pressure in the Eastern Mediterranean, which also shows a long-term trend. There has been also a long-term warming trend in the Eastern Mediterranean, adding to the drawdown of soil moisture. No natural cause is apparent for these trends, whereas the observed drying and warming are consistent with model studies of the response to increases in greenhouse gases. Furthermore, model studies show an increasingly drier and hotter future mean climate for the Eastern Mediterranean. Analyses of observations and model simulations indicate that a drought of the severity and duration of the recent Syrian drought, which is implicated in the current conflict, has become more than twice as likely as a consequence of human interference in the climate system.

Keywords: Syria; climate change; conflict; drought; unrest.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Fig. 1.
Fig. 1.
(A) Six-month winter (November−April mean) Syria area mean precipitation, using CRU3.1 gridded data. (B) CRU annual near-surface temperature (red shading indicates recent persistence above the long-term normal). (C) Annual self-calibrating Palmer Drought Severity Index. (D) Syrian total midyear population. Based on the area mean of the FC as defined by the domain 30.5°N–41.5°N, 32.5°E–50.5°E (as shown in Fig. 2). Linear least-squares fits from 1931 to 2008 are shown in red, time means are shown as dashed lines, gray shading denotes low station density, and brown shading indicates multiyear (≥3) droughts.
Fig. 2.
Fig. 2.
(A) Observed winter (November−April) precipitation climatology, 1931–2008, UEA CRU version 3.1 data. (B) The spatial pattern of the CRU change in 6-month winter precipitation from 1931 to 2008 based on a linear fit (shading); those GHCN stations that indicate a significant (P < 0.1) trend over their respective records are shown as circles and crosses (indicating drying/wetting). (C) The difference in liquid water equivalent (LWE) between 2008 (annual) and the mean of the previous 6 years using the NASA GRACE Tellus project data. (D) The difference in the Normalized Difference Vegetation Index (NDVI) between 2008 (annual) and the mean of the previous 7 years.
Fig. 3.
Fig. 3.
(A) Timeseries of observed (CRU) 3-year running mean 6-month winter FC (area mean) precipitation: total (red), CO2 fit from regression (black), and the residual or difference between these (dashed blue). Frequency distributions based on gamma fits of 3-year running mean 6-month winter FC (area mean) precipitation, for the (B) observed data (corresponding with above) and (C) CMIP5 model simulations, comparing historical and histNat runs. Quantile thresholds based on the total (in B) and historical (in C) are shown at 2%, 5%, and 10% (dotted lines). The tables indicate the percentage of actual (B) observed (sample size 76) and (C) model simulated (sample size 46 × 72 for histNat and 69 × 72 for historical) occurrences exceeding the respective thresholds.
Fig. 4.
Fig. 4.
The 6-month winter low-level (850 hPa) horizontal winds (arrows) and specific humidity (shading) for the period 1931–2008. Shown are the (A) climatology, (B) composite difference between driest and wettest years (those outside of ±1 SD) and (C) the change, or difference between the recent 20 years and the 20 years at the beginning of the period.
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