Precipitation Drought Research Articles

CLIMATOLOGY OF PRECIPITATION DROUGHTS IN ILLINOIS BASED ON WATER SUPPLY PROBLEMS

Drought begins with a reduction in precipitation, but different kinds of precipitation deficiency episodes (duration, intensity, and areal extent) create varying problems for drought-sensitive activities; an agricultural droughttypically is not a water supply drought. Shared characteristics of precipitation deficiency events and related surface water supply problems in Illinois were used to define climatological characteristics of precipitation deficiency droughts that cause problems for water supply systems. The temporal and spatial characteristics of these water supply precipitation droughts were assessed revealing that droughts typically: (a) begin in warm season months; (b) become more widespread when more severe and/or of shorter duration (although all droughts could be expected to cover at least 75%-85% of the state); (c) are more severe and frequent in central Illinois; and (d) end with much above normal precipitation in the initial post-drought months, but tend to recess to slightly drier than nor...

Early growth patterns of red alder and black cottonwood in mixed species plantations

Growth patterns of black cottonwood (Populus trichocarpa Torr and Gray) cuttings and red alder (Alnus rubra Bong.) wildlings were studied during the first year after planting on low elevation glacial till soils in western Washington, USA. Black cottonwood height growth occurred earlier, with 88% of its height having been achieved by late July (Julian day 210). Red alder growth continued longer with 55% of its height growth achieved after late July. Leaf area ratios were consistently higher throughout the season for black cottonwood than for red alder - a maximum of 42 square cm/g for black cottonwood and 29 square cm/g for red alder. Growth parameters in both species were adversely affected by periods of no precipitation and soil drought. Biomass production for the first year was low - 0.04 metric tons per hectare for black cottonwood and 0.74 metric tons per hectare for red alder compared to other studies in the region where black cottonwood and red alder were planted to closer spacings. The general ability of black cottonwood to achieve its growth earlier in the season coupled with greater leaf area ratio may explain its different behaviour from red alder in mixed stands.

Studies on droughts of Tamil Nadu with special reference to their spread and severity

Droughts, generally understood as a period of dryness due to lack of rain is inter preted variously depending on the normal climatic conditions, available water resources, agricultural practices and economic activities of the region. Depending on the purpose of study and basic criteria chosen, all the concepts and definitions regarding droughts may be classified as precipitation droughts, atmospheric droughts, agricultural droughts and hydrologic droughts.
 
 Most of the literature on droughts is based on the analysis of precipitation and temperature records -the statistical techniques are quantitative and often lack the physical basis while the non-statistical ones are empirical. On the other hand, Thornthwaite's water budget method is quantitative and based on a sound and rational physical approach. According to this, drought cannot be defined in terms of rainfall deficiency alone, without taking into account the water need of the region and the role of soil moisture.
 
 In the present study, droughts during the period 1901-1975 over Tamil Nadu and vicinity have been analysed by the application of the water balance approach. Droughts, however, require extended periods of time to develop as they are usually the culmination of a set of weather sequences. Aridity, anomaly diagrams on a yearly basis have, therefore, been drawn which show annual fluctuation in aridity presumably caused by large-scale changes in general circulation of the atmosphere. With the annual patterns as a basis, drought spread diagrams on a monthly basis have been drawn to identify the 'cove' areas and periods.
 
 After identifying the drought spells of various intensities and their spread, the cumulative effect of these water deficiencies in dry spells were assessed by employing the cumulative deviation technique. This method besides giving an objective assessment of drought severity, also indicates the beginning, duration and end of a drought spell- the components of a regular life cycle.

Removing the Confusion Over Droughts and Floods: The Interface Between Scientists and Policy Makers

Droughts and floods, as precipitation excesses, are quite different natural hazards, and each costs the United States more than $1 billion in losses annually. At the impact and policy levels, confusion arises from an inability to define droughts suitably and to identify flood losses in a quantitative way, unaffected by population changes, land use shifts, and other socioeconomic factors. Examples from Illinois research are used to show how relationships can be developed between generally understandable precipitation values and drought or flood losses in various economic sectors and land use areas. Then, the time and space variations of the events can be objectively assessed by using the precipitation data, providing meaningful scientific-engineering definitions for use by decision makers.