Drought Frequency Analysis in Tlamacazapa , Guerrero, Mexico
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Transcript of Drought Frequency Analysis in Tlamacazapa , Guerrero, Mexico
Drought Frequency Analysis in Tlamacazapa, Guerrero, Mexico
Robin LynchHydrology
April 29,2010
Tlamacazapa, Guerrero
Remote mountain village
Extreme poverty
Water scarcityReliant on
wells contaminated with arsenic
Source: Google Maps
Previous Work
Concluded:Year round
piped water possible…but
Needs 10 meter high dam downstream
Source: Google Earth
Assumptions:Only used average rainfall between
2003-2007 Doesn’t take into account long term
variability!
0
50
100
150
200
250
Aver
age
Rai
nfal
l (m
m/m
onth
)
Drought Frequency AnalysisDetermine how impacted Tlamcazapa is by
droughtsUse SPI (Standardized Precipitation Index)
Assumes data is normally distributedSource: (Hallack-Algeria 2005)
Instituto Mexicano de Technologia del Agua (IMTA)16 gaging stationsWithin 25 kilometer radius of TlamaRainfall data between 1940-1998Inconsistent years in each station
First station
Source:(McKee et al. 1993)
Second Station
Whoa!!!
Theissen PolygonsCannot take average of SPI per yearEach gage’s SPI thrown off due to
incomplete time spanMust use Theissen Polygons to
choose Nearest NeighborFor years when closest gage has no
data, use nearest neighbor “hot decking” imputation procedure
60+ years of Data!Data from 1940-2007 (1944,1946,1999-2002 missing)
Check for Normality
…It’s Kinda Normal
SPI Values for Tlama: 1940-2007
HEC-SSP Only looks at probability of
exceedence
Probability Distribution Function
Drought Magnitude
1940
1942
1945
1948
1950
1952
1954
1956
1958
1960
1962
1964
1966
1968
1970
1972
1974
1976
1978
1980
1982
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1998
2004
2006
0
0.5
1
1.5
2
2.5
3
3.5
4
4.5
Drought Magnitude
Dro
ught
Mag
nitu
de (
Sum
of
SPI)
Source: (McKee et al. 1993)
Recurrence Probability
P(SPI<0) = 0.5P(SPI<-1)= 0.15P(SPI<-1.5)= 0.1
Drought Frequency of Tlama
Single Year 2 Cons. Years 3 Cons. YearsMild Drought 2 4 8
Moderate Drought 7 44 296Severe Drought 10 100 1000
Extreme Drought 20 400 8000
Return Period
Future WorkStatistical regression to see the
relationship between drought and arsenic levels
Make recommendations for reservoir planning using this drought frequency analysis