Agricultural drought index and monitoring on national scale

LU HouquanNational Meteorological Center, CMA

Contents• Agricultural drought disasters in China• Agricultural drought indices

--Precipitation anomalies --Soil moisture--Remote sensing drought index--Crop Water Deficit Index--Integrated Drought Index

• Integrated agricultural drought monitoring

0

20

40

60

80

100

19501954195819621966197019741978198219861990199419982002

year

Percentage(%)

The area of cropland damaged by drought was on the range from 40% to 80%,occupying that caused by weather disasters（Data from the National Statistic Bureau)

Part 1: Agricultural drought disasters in China

Agricultural drought with seasonal and regional feature in China

Due to:• Several climate types (uneven distribution of

precipitation on spatial and temporal, large variability)

• Various agriculture styles in different regions (crop varieties, cropping system, water requirement for various crops)

• Different water supply conditions for agricultural crops

Seasonal agricultural drought• Spring drought: impacting on winter wheat and other

crops sowing in northern China, and impacting on rice transplanting in southern China

• Early summer drought: impacting on some crops sowing and autumn-matured crops in northern China

• Midsummer drought: impacting on rice in southern China• Autumn drought: impacting on winter wheat sowing in

North China• Winter drought: impacting on over-winter crops in South

China

Part 2: Agricultural drought indices

The main factors related with agricultural drought

• Climate (evaportranspiration, precipitation)

• Soil (type, moisture)

• Crops (species, stage of development)

• Irrigation capacity (facilities , water resource)

--Precipitation anomalies (PA)

Pa is percentage of precipitation anomalies(%)； is climatic normal of precipitation (mm) of the 30 days ，P is precipitation of 30 days (mm)

• Advantage: observable, denoting storage of water for agriculture, especially for rainfed farming

• Disadvantage: can’t reflect water consumption and water demand of crops

Agricultural drought index

%100

PPPPa

P

Agricultural drought index-- Relative soil moisture (RSM)

Rw is relative soil moisture（%）；W is soil moisture on weight percentage（%），fc is field capacity（%）

• Advantages : measurable and simulated, expressing how much available water in soil for crops

• Disadvantage: with a poor representativeness on spatial, can not be use to paddy field

%100cfwRw

Agricultural drought index--Crop Water Deficit Index (CWDI)

• CWDIi is crop water deficit index of 10 days, ETa is actual evapotranspiration of 10 days, P and I is precipitation and irrigation of 10 days, ai is weight coefficient

• Advantages: to judge if precipitation and irrigation could meet the water demand of crops or not

• Disadvantage: unmeasured, can’t express other factors influence on water consumption and with many coefficients

a

ai ET

IPETCWDI

n

iii CDWIaCDWI

1

Crop water requirement

ETa= Kc·ETo

ETa = crop water consumption (evapotranspiration)Kc = crop coefficientETo = reference crop evapotranspiration

• FAO Penmen-Monteith Equation for ETo

Rn = net radiation at crop surfaceG = soil heat fluxT = mean daily air temperature at 2 m heightU2 = wind speed at 2 m heightes - ea = saturation vapour pressure deficit∆ = slope vapour pressureγ= psychrometric constant

)34.01(

)(273

900)(408.0

2

2

U

eeUT

GRET

asn

o

--Remote sensing drought indices

Integrated by Thermal Inertia method, Crop Water Stress Index ,Temperature and Vegetation Drought Index

• Advantages: observable, continuously on spatial, reflecting status of soil moisture and crops response to water supply

• Disadvantage: impacted by cloudy and vegetations on ground, data source unstable

n

iii wfDRG

1

Agricultural drought index

--Integrated Drought Index

• For various regions and cloud status, precipitation anomalies, soil moisture, CWDI and remote sensing indices would be given different weighting.

Agricultural drought index

n

iii DIfIDI

1

Agro-climatic zoning of China

LAI

Kc

CNDI weight

Remote Sensing

Precipitation anomalies

Crops water deficit

Soil moisture

Integrated drought index

In Soil –plant-atmosphere continuum , overall agricultural drought monitoring

Part 3: Integrated agricultural drought monitoring

Flow chart

Soil moisture Index

Crop water deficitIndex

Remote SensingDrought Index

Dynamic soil moisture model

Dynamic CWDIDrought model

Remote SensingDrought model

Soil moistureSoil textureCrop stage

Mete. dataCrop stage

NOAA、EOS/MODIS、FY-1、FY-2C

Integrated agricultural drought model on region scale

Agricultural drought monitoring system on GIS

Agricultural drought monitoring operation

Products of Agricultural drought monitoring

Mete. data

Precipitationanomalies

Moving preci.anomalies

On the GIS, integrated agricultural drought monitoring system

Surface agricultural drought monitoring system

Remote sensing monitoring system

Integrated monitoring system

Case on 1st decade Aug.2006

Remote Sensing

Soil moisture

Integrated monitoring

Crop water deficit

Soil moisture simulation

Remote Sensing

Soil moisture Crop water deficit

Integrated monitoring

Precipitation anomalies

Case on 1st decade Jan. 2009

Agricultural drought monitor and prediction on national scale product released by NMC