7.2 Forecasting in the Central Asian Hydromets
7.2.1 Background
The key agencies that that are charged in predicting river discharge regularly in Central Asia are the Hydrometeorological Agencies. For predicting mean discharge over a certain future period, they use different types of statistical models.
The particular type of model they use depends on the available hydrological and meteorological data for a particular river whose mean discharge is to be forecasted and on the type of the forecast. Types of forecasts include
- daily forecasts, i.e. \(\Delta t = 1 \text{ day}\),
- pentadal forecasts, i.e. \(\Delta t = 5 \text{ days}\),
- decadal forecasts, i.e. \(\Delta t = 10 \text{ days}\),
- monthly forecasts, i.e. \(\Delta t = 1 \text{ month}\), and
- seasonal forecasts, i.e. \(\Delta t = 6 \text{ months}\).
To this date, these types of forecasts are performed at regular intervals by the operational hydrologists. Normally, this requires normally a lot of manual work. Recently, selected Hydrometeorological Agencies use automated software to automatize this type of work17.
In Uzbekistan, for example, the following list of forecast objects exists in the Hydromet.
| River | Gauge (Target Object) | Gauge Code | Country | Types of Forecasts |
|---|---|---|---|---|
| Chirchik | Inflow to Charvak Res. | 16924 | UZ | dl, m, s |
| Chirchik | Inflow to Charvak Res. + Ugam River | 16924 + 16300 | UZ | m, s |
| Akhangaran | Irtash | 16230 | UZ | m, s |
| Chadak | Dzhulaysay | 16202 | UZ | m, s |
| Gavasay | Gava | 16193 | UZ | m, s |
| Padsha-Ata | Tostu | 16176 | KG | m, s |
| Kara Darya | Inflow to Andizhan water reservoir | 16938 | UZ/KG | dl, m, s |
| Isfayramsoy | Uch-Kurgan | 16169 | KG | m, s |
| Sokh | Sarykanda | 16198 | UZ | dl (May - Sep.), m, s |
| Sanzar | Kyrk | 16223 | UZ | m, s |
| Naryn | Inflow to Toktogul water reservoir | 16936 | KG | m, s |
| Vaksh | Inflow to Nurek water reservoir | 17084 (Vakh river - Darband gauge) | TJ | m, s |
| Kafirnigan | Tartki | 17137 | TJ | m, s |
| Tupalang | Inflow to Tupalang water reservoir | 17194 | UZ | m, s |
| Sangardak | Keng-Guzar | 17211 | UZ | m, s |
| Akdarya | Inflow to Gissarak water reservoir | 17464 (Akfariya river - Hissarak gauge) | UZ | m, s |
| Yakkabagdarya | Tatar | 17260 | UZ | m, s |
| Uryadariya + Kichik Uryadariya | Inflow to Pachkamar water reservoir | 17279 (Uryadariya river - Bazartepe gauge) + 17275 (Kichik Uryadariya - Gumbulak gauge) | UZ | m, s |
| Zeravshan | Inflow to Rovatkhodzha hydro work | 17461 | UZ | m, s |
It should be noted that all of the Hydromets have such type of lists with different forecast target and types. As can be seen from the above list, Uzbekistan does neither issue pentade nor decadal forecasts, i.e. types of forecasts which are widely used in the Kyrgyz Hydromet in contrast.
Finally, seasonal forecasts in the Uzbek Hydromet are issued twice prior to the irrigation season with 3. - 5. March being the first issues data range and 3. - 5. April being the second one. Converse to this, monthly forecasts are issues between the 25. - 27. day each month. Finally, decadal and pentade forecasts are issued each morning at the day of the end of the corresponding pentade or decade.
It is important to emphasize again that there is currently no standardized way in the region to produce these forecasts. While in some instances, a particular approach and method works very well, it fails to produce acceptable forecasts in other basins. However, as we shall see, certain techniques work very well for particular forecast horizons which then explains why such type of technique has become widely used in the region.
7.2.2 Forecasting for What and Whom?
Why is all this work is required? What is the purpose of predicting mean discharge into the future at regular intervals? Important recipients of the forecast products include the Water Authorities which are in charge of delivering adequate amounts of water for irrigation at the right time and location.
It all starts with pre-season irrigation planning. The main irrigation season in most of Central Asia is from April 1. through the end of September. Previous to the start of the irrigation season, irrigation plans are drafted based on computed irrigation water demand of all the water users that are connected to a particular irrigation system. These irrigation system are defined in terms of canal topology where demand gets aggregated from the bottom up to the Rayvodkhozes and the Oblvodkhozes. The later then starts with the pre-season irrigation planning given the water irrigation system-level demand. These plans specify decadal water discharge for each irrigation system and the corresponding canals.
Demand is one thing, but expected supply from the Central Asian rivers another. In order to be able to match the irrigation water demand, the water authorities do what is needed and receive from the Hydromets first the seasonal discharge forecasts. Given this forecast of irrigation-season water availability, the water authorities then adjust their plans given the particular expected circumstances. If, for example, an exceptionally dry year is expected, they activate limit plans and reduce planned water distributions according to forecasted quantities. If a wet year is expected, they do not perform these adjustments and maybe even release water from reservoirs previous to the irrigation season to ensure enough storage capacity in the reservoirs.
With the beginning of the irrigation season, another seasonal forecast is carried out by the Hydromets and communicated to the Central Asian water authorities. Given the updated forecast, planning is revised and adjusted accordingly. Then, finally, throughout the irrigation season pentadal, decadal and monthly forecasts are produced constantly to carefully balance water demand with supplies while the season is under way.
Needless to say that other important customers for hydrometeorological forecasts exist, including for example airports, road departments that need to ensure road safety, agricultural clusters that are interested in frost and hail warnings, local authorities that need to be alerted in the case of extreme local weather conditions, etc.
The software used is called iEasyHydro and currently operationalized in the Kyrgyz Hydromet. Other Hydromets are testing the software (as of 2020). More information about iEasyHydro can be obtained by contacting the author.↩︎