Laserfiche WebLink
<br />Historical Perspectives on Colorado Drought <br /> <br /> <br />, <br /> <br />regional variation. Documents providl...-d by the National Drought Mitigation Center <br />(NDMe 2003) provide further insight into this multifacclt.>d phenomenon. <br /> <br />Drought is a normal, recurrent feature of climate. although many erroneously <br />consider it a rare and random event. It occurs in virtually all climatic zones, <br />but its characteristics vary significantly from one region to another. Droughl <br />is a temporary aberration; it differs from aridity. which is restricted to low <br />rainfall regions and is a permanent feature of climate. <br /> <br />Its <br /> <br />Drought should not be viewed as merely a physical phenomenon or natural event <br />impacts on society result from the interplay between a natural event (less <br />precipitation than expected resulting from natural climatic variability) and the <br />demand people place on water supply. Recent droughts in bolh developing and <br />developed countries have underscored the vulnerability of all societies to this <br />"natural" ha7.ll.rd. Clearly defining drought is a multi-faceted problem. <br /> <br />How <br /> <br />The National Drought Mitigation Center classifies meteorological, agricultural and <br />hydrological droughts as "operational definitions of drought". The Nn~'fC (2003) <br />proves to be an invaluable reference, providing four informative operational <br />definitions of drought. Figures 6-8 illustrate the causes and eITects associated with <br />these delinitions. <br /> <br />(Operational definitions) <br /> <br />is drought classified? <br /> <br />Meteorological drought is usually an expression of precipitation's departure <br />from normal over some period oftimc. These definitions arc usually region- <br />specific, and presumably based on a thorough understanding of regional <br />climatology. The variety of meteorological definitions from different <br />countries at different times illustrates why it is folly to apply a definition of <br />drought developed in one part of the world to another: <br /> <br />~r" ~ -,-_ .... <br /> <br />f-'~ . a.:c> "f/ <br />. .~. ~\;..\ <br />~....., '-.*Y <br />, C-I'iI' .} , <br />..' <br />..f'! \ ~L~~. <br />---- 1( '4 <br />------- <br />------- <br />. .. ... <br />- ~ ~ .. ~. - - <br />- . . . . . - <br />- ,. .. ... ~. ... - <br />drou2h <br /> <br />--- <br />~'_i .1~ <br />..- <br /> <br />Great Britain (1936): 15 consecutive days <br />with daily precipitation totals of less than <br />0.25 mm <br />(1964): <br /> <br />. <br /> <br />80 <br /> <br />period of six days without <br /> <br />a <br /> <br />Meteorological measurements are the first <br />indicators of drought. <br /> <br />J.'i~ure b. :\lap of mefeorolo2ica <br />conditions (:'iOAA-"'CnC 2003) <br /> <br />s <br /> <br />Page 10 <br /> <br />recycled contenl paper <br /> <br />HDR Engineering. Inc. <br />Printed on 30% post-consumer <br /> <br /> <br />than <br /> <br />rainfal <br />the mean <br /> <br />less <br /> <br />rainfal <br /> <br />India (1960): actual seasonal <br />deficient by more than t"vice <br />deviation <br />(1964): <br /> <br />annual <br /> <br />Libya <br />mm <br /> <br />Bal <br />rain <br /> <br />. <br /> <br />. <br /> <br />. <br /> <br />AgriclJllural drollglu occurs when there is not <br />enough soil moisture to meet the needs of a <br />particular crop at a particular time. <br />A~'licultural drought happens after <br />meteorological drought but before hydrological drought. Agriculture <br />usually the first economic sector 10 be affected by drought. <br />