## Procedures for Drought Monitoring

At early stages of studying droughts in Russia, much effort was directed to the development of argometeorological indices to assess drought conditions. Russian scientists have developed more than 50 indices (Ivanov, 1949; Koloskov, 1958; Konstantinov et al., 1976; Loginov et al., 1976; Drosdov, 1980; Ulanova, 1988; Khomyakova and Zoidze, 2001). However, in this chapter we discuss only those indices that are widely used for drought monitoring in Russia.

Hydrothermal Coefficient

A hydrothermal coefficient (HTC) developed by Selyaninov (1928) is widely used to monitor droughts in Russia. The HTC is defined as

where p is monthly precipitation in millimeters and T is temperature in degrees Celsius, i is the ordinary number of a dekad (10-day period) to be estimated, and £ T>10°C is the sum of temperatures above or equal to 10°C.

### Moisture Index

Moisture index (Md) was developed by Shashko (1985) and is also widely used. It is the ratio between the total precipitation during a month and the diurnal mean values of water vapor deficit (the diurnal mean deficit sum of air humidity), as expressed by the following:

where £ R is the precipitation sum in millimeters, and £ d is the sum of water vapor pressure in air (the sum of air humidity deficits) in hecto Pascal (hPa).

Water Supply Index

The water supply index (Vi) is calculated as

where W means water storage in the corresponding soil layer available to plants, 0-100 (i — 1) is the index showing thickness of relevant soil layer, and i is the number of the dekad.

The above indices are widely used in all CIS countries. In Ukraine the drought conditions are also estimated from the index developed by Dmitrienko (1978, 1992):

£ = n(W)3 + n(T)n(R) [1 — y(d)] (1 — 3) [15.4]

where £ is the complex dryness index in terms of relative crop yield; n(W) is the field crop productivity coefficient derived from soil water reserves, W; 3 is the weight coefficient; n(T), n(R) are the temperature, T, and precipitation, R, coefficients of field crop productivity; and y is the index of crop depression from the hot wind impact, d.

Drought Index

Specialists and scientists working in the field of agrometeorology accept the drought index developed by Ped (1975):

where Si is the drought index which is the sum of anomalous weather conditions, i is the site; t is the time; AT is the mean air temperature deviation from the normal (TN) during a period T; AR is the deviation in precipitation from the normal (RN) during a period (R); AE is the deviation of moisture reserves in a 1-m soil layer (E) from the normal (En); and a T, aR, and aE are the root-mean-square deviation in temperature, precipitation, and moisture reserve, respectively.

Zoidze and Khomyakova (2000) analyzed the above indices and also the following indices to describe drought conditions: (1) maximum air temperatures above 30, 35, 40, and 45°C in dekads, (2) rainless periods of different durations, (3) relative air humidity of 30% or less, (4) productive moisture reserves in the 0-20 and 0-100 cm soil layers during winter, early and later spring cereals at the beginning of sowing and mass development phase as well as for individual vegetation months of these crops, (5) water vapor saturation deficit in air at 1500 h at various wind velocities, and (6) crop yield deviations depending on arid conditions.

Until 1917, the Science Committee of Meteorological Agency of the Central Land Organization and Farming Administration monitored droughts in Russia and published map showing probability of dry dekads in the European Russia (Brounov, 1913); a dekad during which the precipitation did not exceed 5 mm was considered a dry dekad. In Soviet and post-Soviet periods, the Hydrometeorological Service monitored drought. This agency collects information about droughts in the Russian Federation regions and submits it to the Ministry of Agriculture and other federal authorities. For the past 20-30 years, the agency has published and updated various agroclimatic reference manuals. For example, two guide books, Agroclimatic Guide Book and Agroclimatic Resources, were published for all regions, territories, and republics of the former USSR. These books show intensity of drought (e.g., weak, moderate, severe, extremely severe) for different regions based on the average number of drought days in a month during vegetation or warm periods and probabilities of drought occurrence.

### Yield Risk Estimation

According to Zhukov et al. (1989), the following equation can be used to estimate the yield risk (i.e., the deviation of expected crop yield from the maximum yield):

where Pj is the pure risk standard of the system climate-yield transition from the initial ith state into the jth state in a given time interval; gj (k) is the transitional probability of the system weather-yield, and k is the dekad number.

Agricultural drought monitoring in Russia has become more systematic after two publications based on ground and satellite data (Zoidze and Khomyakova, 2000). In the first publication, degree of aridity was determined with the help of a mathematical model based on an image recognition procedure (Danielov and Zhukov, 1984; Zhukov et al., 1989; Zhukov and Svyatkina, 2000). Zoidze and Ovcharenko (2000) prepared a map showing the distribution of the degree of aridity in the Russian Federation regions based on an aridity index. The index value was more than 60 (highest) for Kalmykia region and between 51 and 60 for Astrakhan region. About 14% of the RF regions had index value greater than 30.

The operative system of drought assessment is a computer-based system that uses agrometeorological data and various drought indices to regularly monitor the onset and development of droughts of different intensity during the entire vegetation period. The following drought indices are used: (1) Selyaninov's HTC, (2) Shashko's index of moisture (Md), (3) Protserov's water supply index (V; Protserov, 1949), (4) the number of days with relative air humidity <30% (N0), (5) the number of days with maximum air temperature > 30°C (NT), (6) productive moisture reserves in soil layers of 0-20 cm (W0-20), 0-50 cm (W0-50), and 0-100 cm (W0-100) under winter, early spring, and late spring grain crops. All of these indices can be determined using standard hydrometeorological data: precipitation (R), air temperature (T°C), water vapor pressure in air (d), productive water reserves in soil (W), the number of days with the relative air humidity <30% (N0), and the number of days with the maximum air temperature >30°C (NT).

Based on the range of the above values, a climatic event can be categorized as extremely severe, severe, moderate, weak, or no drought (table 15.3). Drought is referred to that category of intensity where its average measure of closeness (P) is maximum:

Table 15.3 Drought categorization based on various indices used in Russia

Category of drought intensity

Drought assessment index

Extremely

No drought Weak Moderate Severe severe (class 5) (class 4) (class 3) (class 2) (class 1)

1. Selyaninov's hydrothermal >0.76 index (HTC)

2. Shashko's index of moisture >0.41 (Md)

4. Number of days with relative 0 air humidity <30% (NO)

5. Number of days with 0 maximum air temperature >30°C (Nt)

6. Productive moisture reserves >21 (mm) in the 0-20 cm soil layer (W0-20)

7. Productive moisture reserves >46 (mm) in the 0-50 cm soil layer (W0-50)

8. Productive moisture reserves >81 (mm) in the 0-100 cm soil layer (W0-100)

0.61-0.75 0.40-0.60 0.20-0.39 <0.19 0.31-0.40 0.20-0.30 0.10-0.19 <0.09 61-70 51-60 41-50

16-20

36-45

61-80

11-15

26-35

41-60

6-10

16-25

26-40