12 Dynamics, Range, and Severity of Hydrological …
231
This may sometimes intensify surface runoff and evaporation, i.e., the processes
conducive to soil drought. If water shortage is translated into measurable losses
manifested by plant degradation and restricted growth or if drought periods overlap
with intense field works, agricultural drought may occur [8]. Individual plant species
show different tolerance to soil water deficiency, which is why the concept of agrometeorological drought involves relationships between precipitation and plant growth
conditions. An official indicator of agricultural drought in Poland is the climatic
water balance (CWB). The metric is used by the Agricultural Drought Monitoring
System
1 that evaluates drought severity between 1st April and 30th September in 13
six-decade periods for various plant species. In communes where CWB threshold
values are exceeded, the monitoring data are the basis for compensation claims.
Further increase of water deficit results in hydrological drought [2, 9–12]. The
non-supplied aquifers are continually drained by watercourses and springs. As a
result, the elevation of their water table declines and low groundwater period occurs.
This is accompanied by a systematic decrease in surface water resources, which are
usually in a hydraulic connection with groundwater. These mechanisms facilitate
the appearance of summer and autumn low flows. Recession rate of the groundwater resources of the active exchange zone in this period, and thus the rate of low
flow development, depend nearly exclusively on the retention level of groundwater
reservoirs [13–15].
Winter low flows of surface waters follow a different course. Limited runoff is
then due to temporary water retention in the snow cover often combined with riverbed
freezing during severe frosts that stops all forms of drainage (Fig. 12.1). This is not
a global problem, but in the countries with a harsh climate, it may severely disturb
water management [16–18]. It is worth noticing that winter drought does not consist
in water shortage but its entrapment in the form of snow and ice. This means it is
highly seasonal and water resources are retained “on the spot”.
Severe hydrological droughts bring about serious losses to water consumers, and
this is why a concept of a socio-economic drought has been coined. The effects
of such a drought may be perceptible at the national scale [10]. Disturbed functioning of water-power engineering or agricultural production affects economy. Water
shortage impacting municipal services management is classified as social effects of
drought, while the degradation of aquatic ecosystems, especially during the blooms
of toxic algae causing significant decline of water quality, is the manifestation of its
environmental effects.
Human activities currently interfere with all stages and links of drought development (see Fig. 12.1), and in some cases, may accelerate its advancement [7].
Agrotechnical treatments aimed at ensuring optimal conditions of plant growth need
to be initiated as soon as rainfall shortage brings about meteorological drought. Irrigation is then intensified by using local groundwater resources and providing water to
plants via sprinkling machines or other forms of watering. Water collected from the
saturation zone does not infiltrate back to the groundwater reservoirs but is removed
during evapotranspiration. This results in simultaneous development of atmospheric
1 https://www.susza.iung.pulawy.pl/en/.
231
This may sometimes intensify surface runoff and evaporation, i.e., the processes
conducive to soil drought. If water shortage is translated into measurable losses
manifested by plant degradation and restricted growth or if drought periods overlap
with intense field works, agricultural drought may occur [8]. Individual plant species
show different tolerance to soil water deficiency, which is why the concept of agrometeorological drought involves relationships between precipitation and plant growth
conditions. An official indicator of agricultural drought in Poland is the climatic
water balance (CWB). The metric is used by the Agricultural Drought Monitoring
System
1 that evaluates drought severity between 1st April and 30th September in 13
six-decade periods for various plant species. In communes where CWB threshold
values are exceeded, the monitoring data are the basis for compensation claims.
Further increase of water deficit results in hydrological drought [2, 9–12]. The
non-supplied aquifers are continually drained by watercourses and springs. As a
result, the elevation of their water table declines and low groundwater period occurs.
This is accompanied by a systematic decrease in surface water resources, which are
usually in a hydraulic connection with groundwater. These mechanisms facilitate
the appearance of summer and autumn low flows. Recession rate of the groundwater resources of the active exchange zone in this period, and thus the rate of low
flow development, depend nearly exclusively on the retention level of groundwater
reservoirs [13–15].
Winter low flows of surface waters follow a different course. Limited runoff is
then due to temporary water retention in the snow cover often combined with riverbed
freezing during severe frosts that stops all forms of drainage (Fig. 12.1). This is not
a global problem, but in the countries with a harsh climate, it may severely disturb
water management [16–18]. It is worth noticing that winter drought does not consist
in water shortage but its entrapment in the form of snow and ice. This means it is
highly seasonal and water resources are retained “on the spot”.
Severe hydrological droughts bring about serious losses to water consumers, and
this is why a concept of a socio-economic drought has been coined. The effects
of such a drought may be perceptible at the national scale [10]. Disturbed functioning of water-power engineering or agricultural production affects economy. Water
shortage impacting municipal services management is classified as social effects of
drought, while the degradation of aquatic ecosystems, especially during the blooms
of toxic algae causing significant decline of water quality, is the manifestation of its
environmental effects.
Human activities currently interfere with all stages and links of drought development (see Fig. 12.1), and in some cases, may accelerate its advancement [7].
Agrotechnical treatments aimed at ensuring optimal conditions of plant growth need
to be initiated as soon as rainfall shortage brings about meteorological drought. Irrigation is then intensified by using local groundwater resources and providing water to
plants via sprinkling machines or other forms of watering. Water collected from the
saturation zone does not infiltrate back to the groundwater reservoirs but is removed
during evapotranspiration. This results in simultaneous development of atmospheric
1 https://www.susza.iung.pulawy.pl/en/.