Spatial patterns of drought in the interior plains of North America

126

This paper analyses the spatial and temporal variability of winter droughts in a semi-arid geographic gradient in Northeast Spain, from the Pyrenees in the north to the Mediterranean coastland in the south. Droughts that occurred between 1952 and 1999 were analysed by means of the Standardised Precipitation Index (SPI). The influence of the weather-type frequency and of the general North Atlantic atmospheric circulation patterns was analysed. The results indicate that winter droughts show an important spatial variability in the study area, differentiating three well-defined patterns. These correspond to the Pyrenees, the centre of the Ebro Valley, and the Mediterranean coastland. General negative trends in winter SPI have been found, which are indicative of the increase in winter drought conditions in the study area. Nevertheless, important spatial differences have also been recorded. Dominant north-south gradients in the influence of weather types are shown. Moreover, the negative trends in winter-SPI values agree with the negative trend in the frequency of the weather types prone to cause precipitation, such as the C, SW and W weather types and the increase in the frequency of A weather types. Nevertheless, in the Mediterranean coastland, the positive trend in SPI values agrees with the increase in the frequency of weather types of the east (E, SE), which are prone to cause precipitation in this area. Interannual variations in the frequency of the different weather types have been highly determined by different general atmospheric circulation patterns, mainly the North Atlantic Oscillation (NAO). Nevertheless, the correlation between the time series of weather-type frequency and the winter SPI is higher than that found between the SPI and the NAO. Thus, although the interannual NAO variability explains a high percentage of the interannual differences in the frequency of different weather types, it is not sufficient to explain the spatial and temporal variability of droughts, which respond better to atmospheric variability at more detailed (synoptic) spatial scales.

Section: Drought Spatial and Temporal Patterns During The Winter Seasonmentioning

confidence: 99%

The influence of atmospheric circulation at different spatial scales on winter drought variability through a semi‐arid climatic gradient in Northeast Spain

Vicente‐Serrano

López‐Moreno

2006

126

“…Previous studies have found that preferred spatial patterns of moisture variability are often linked to a particular set of causal mechanisms (Oladipo, 1986;Nkemdirim and Weber, 1999). Therefore, the relationships between the main spatial modes of June-July moisture variability (as determined by the PCA) and a variety of atmospheric, oceanic, and surface-condition data were examined.…”

Section: Investigating Possible Causal Mechanisms Of Moisture Anomaliesmentioning

confidence: 99%

Characterizing the spatial and temporal variability of June–July moisture conditions in the Canadian prairies

Quiring

Papakyriakou

2005

Palmer's moisture anomaly index (Z-index) was used to characterize the frequency, severity, and spatial extent of June-July moisture anomalies for 43 crop districts across the Canadian prairies during 1920-99. In addition, the main modes of spatial and temporal variability in moisture conditions were identified and used to elucidate the physical mechanisms responsible for causing these moisture anomalies to occur. The crop districts were divided into five relatively homogeneous moisture regions using cluster analysis, and moisture anomaly statistics were analysed for each region.The single most severe June-July drought on the Canadian prairies occurred in 1961. This drought covered more than 86% of the study region and had a mean severity (Z-index) of −5.67. Other severe June-July droughts occurred in the Canadian prairies (in order of severity) in 1988, 1936, 1929, and 1937. The results demonstrated that the severity and spatial extent of moisture anomalies on the Canadian prairies are strongly correlated, indicating that the more severe events tend to affect larger areas. The most drought-prone regions experienced moisture conditions detrimental to crop production in approximately one year out of every six years.The spatial analysis revealed the existence of three preferred spatial patterns of moisture variability on the Canadian prairies and each pattern can be attributed to a unique set of atmospheric and oceanic forcings. The temporal analysis verified the presence of coherent periodicities (in particular quasi-2, -4, and -10-15 year oscillations) in the moisture time series.

“…Past examinations of spatial and temporal extents of drought have been numerous (e.g., Skaggs, 1975;Klugman, 1978;Karl, 1983;McGregor, 1985;Oladipo, 1986;Soulé and Meentemeyer, 1989), while examinations of wet periods have been fewer in number (e.g., Diaz, 1983;Fye et al, 2003). Fye et al (2003) indicated that during the past 500 years only three pluvials may have equaled that of the early 20th century occurring from 1549-1558, 1602-1622 and 1825-1840.…”

Section: Introductionmentioning

confidence: 99%

Characteristics of US drought and pluvials from a high‐resolution spatial dataset

Kangas

Brown

2007

Abstract:Anomalous precipitation can be a devastating natural disaster having significant impacts on economies, society and the environment. This study examines the spatial and temporal characteristics of anomalous precipitation throughout the United States to obtain a greater understanding of drought/pluvial regimes, including intensity, duration and spatial coverage based on a high-resolution precipitation dataset. With the help of the parameter-elevation regression on independent slopes model (PRISM), approximately 4 km data for the United States is used to construct the Palmer drought severity index (PDSI) and the standardized precipitation index (SPI) for the period 1895-2003. Increased resolution from the PRISM dataset shows that drought/pluvial areas are not as homogeneous as seen in previous studies based on climate divisions and larger scales. While size, duration and locations of drought/pluvial events are influenced by the index used, the largest annual drought/pluvial events occur more frequently in the central United States, with a higher percentage of extreme values occurring in the western portion of the country. Four large pluvial events have occurred in the United States during the study period, with three of these having occurred during the past 30 years.