function?run=droughtrun（spi）
%?the?input?must?be?a?col?vector
spi=spi‘;
x0=0;
x1=-0.3;
x2=-0.5;
indx=find（spi<=x1）;
%?the?location?where?spi<=x1?
lspi=[indx;spi（indx）];
%?the?first?row?represents?location?where?spi<=-0.3?and?second?row
%?are?spi?values?via?reletive?lacation
j=[];
for?i=2:length（indx）-1
????if?（lspi（1i+1）-lspi（1i））>1?&&?（lspi（1i）-lspi（1i-1））>1;
????????j=[ji];
????????%?find?the?single?drought?evedent
????end
end
for?k=1:length（j）
????if?lspi（2j（k））>x2?
????????%?judge?whether?consider?the?single?drought?event?as?drought?occurrence
????????lspi（2j（k））=0;
????????%?assign?0?to?these?single?drought?events?which?was?not?considered?as?drought?occurrence
????end
end
ind=find（lspi（2:）~=0）;
%?delete?the?non-drought?events
lspi=lspi（:ind）;
k=[];
for?i=1:length（lspi（1:））-1;
????if?lspi（1i+1）-lspi（1i）==2;?
????????%?尋找兩次干旱事件之間只間隔一月的間隔月
???????k=[ki];?
????end
end
ls=[];
lspi=lspi‘;
spi=spi‘;
for?i=1:length（k）
????if?spi（lspi（k（i）1）+11）????????%?判定是否將間隔月定位干旱事件
????????ls=[ls;lspi（k（i）1）+10];
????????%?將干旱事件整合
????end
end
lspi=[lspi;ls];
ls1=lspi（:1）;
[yind]=sort（ls1）;?
z=zeros（length（y）1）;
for?i=