Susze rolnicze
Zarys problematyki oraz metody monitorowania i klasyfikacji

S u m m a r y

Drought is a multi- and inter-disciplinary phenomenon and - as it is stated in the literature - there is no possibility and necessity for a unique and universal definition of drought. The definition should be formulated in the perspective of a given discipline (meteorology, hydrology, pedology, agriculture, socio-economic). According to this there are many parameters and indices of droughts. Meteorological drought indices should be the basic and the preliminary for agricultural drought risk assessment. Agricultural drought is a relative phenomenon and its evaluation should be done in relation to a given crop, soil and region. Crop yield reduction is recognized as the most important and ultimate index of the effect of agricultural drought.

In the monograph different indices of meteorological, soil and agricultural droughts are analyzed and evaluated. Among others they are:

• standardized precipitation index SPI,
• relative precipitation index,
• precipitation at a given probability of non-exceedance,
• the ratio of actual soil water content to hardly available soil water,
• reduction of evapotranspiration due to soil water deficit,
• reduction of crop yield,
• crop water deficits.

On the basis of the analysis carried out, the classification of agricultural droughts are proposed in relation to the above indices.

In agricultural drought monitoring the in-field (on-ground) infrared thermometry of crop canopy can be useful. In the study the empirically determined parameters and relationships are presented for different crops.

Finally the importance and possibility of usage of modeling of processes in soil-plant atmosphere continuum in drought monitoring is emphasized. Models for operational predicting of irrigation requirements and irrigation control, developed by the author and being in use in Poland, are presented in detals.

Moreover this monograph characterizes droughts in Poland, emphasizing the natural conditions for their occurrence, their frequency, extent, the damage they cause and the resulting consequences for agriculture.

Poland is situated in a transitory temperate climate zone, nonetheless droughts occur posing a serious economic, social and environmental problem. Droughts in Poland have a character of atmospheric anomaly following the rainless period. In dependence on the amount of precipitation deficit and on its long-term, annual or seasonal distribution we are dealing with the hydrologic, atmospheric or soil drought. The direct effect of a drought is a disturbance in the water budget of an area caused by a precipitation deficit and a large amount of evaporation (atmospheric drought), which is manifested by excessive soil drying (soil drought) and by lowering the ground water table and decreasing water flow in rivers (hydrologic drought).

Droughts in Poland are hardly predictable. It is difficult to forecast the term of their occurrence, duration, territorial range and intensity. This leads to trouble in operational planning and in undertaking the proper advance measures to mitigate the negative effects. In spite of this unpredictability and irregularity of drought occurrence in Poland, one may observe some statistical properties of their frequency, duration and the regions affected.

Drought phenomena in Poland have been recorded in the chronicles since the fourteenth century and were found to occur many times a century. It is assumed that droughts appear in Poland once every 4-5 years. The driest region of Poland is almost the entire central region, as well as northwestern and mid-eastern parts. These are the regions most threatened by droughts. The most frequent and most severe droughts occur in this area, which sometimes experience extremely long periods without rain.

Various preventive measures are undertaken to mitigate the harmful effects of droughts. The most important is the development of water resources, especially on agricultural lands. To accomplish this aim, small scale water retention projects have been elaborated and are under implementation in many provinces of Poland. Irrigation plays an important role in mitigating the effects of drought on crop production. Water management for irrigation is one of the most important issues in dealing with droughts. Problems concerning the effective use of irrigation water and the optimization of water distribution are being addressed. Crop rotation, rehabilitation and modernization of the existing irrigation systems and soil reclamation are other measures that can reduce the harmful effects of droughts on agriculture. Various methods to conserve water in agriculture are used i.e. increasing the productivity per unit of water used, reducing non-beneficial uses or relocating uses from low to high value crops.

The pressure for increased water supplies is intensifying in Poland. That is why there is an urgent need to improve the uniform national strategy of drought mitigation including a national water saving policy and its legal aspects, the issuing of drought advisories and warnings, the creation of guidelines on how to prevent and counteract the effects of drought and to release recommendations stating the tasks and the most adequate measures to be undertaken. They should be addressed in long-term strategy for drought control. Preparation of such a strategy together with programs for the accomplishment of the relevant tasks is indispensable in the nearest future in Poland.