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E. Tomaszewski and M. Kozek
drought and low flows of low groundwater levels, often without the soil drought
stage. At the next stage, groundwater resources are exhausted, and surface water
reserves need to be mobilized to mitigate the soil drought. However, by this time
the drought severity is so strong that water redistribution quickly leaps from local to
regional scale and results in low flow of rivers. As a result, when the hydrological
drought should only naturally begin, low flows of underground and surface waters
are already highly advanced.
Many regions of the world, where the effects of drought are particularly harsh or
dangerous, introduced early warning systems. They improve and implement methods
for short-term and seasonal forecasting of drought and develop an integrated information exchange system between networks. They include various scenarios of drought
development and emergency plans at the state and regional levels. The systems also
assess the risk of individual events and available insurance options [19]. Drought
risk assessment in Poland involves not only the strategies of mitigating its effects but
also the process of drought risk management [20].
12.2 Methodology and Data
River low flow, i.e. the last stage of the response to insufficient supply, is considered
a good indicator of hydrological drought [21–23]. It is usually defined as a period
of low flows (water levels) in a river or flows maintained during dry weather [14,
24]. Precise definition of the low flow depends on a specific research approach.
One of them is a threshold level method in which an analysis of a flow hydrograph
with respect to a threshold value determined based on a selected characteristic flow
enables identification of the low flows. Limit values are estimated based on second
degree main flows, periodic flows from the flow duration curve, analysis of annual
minima distribution or conventional flows adapted to specific challenges of water
management and environmental management. In this research approach, the low
flow is a period with flows lower than the established threshold flow [25–27]. As a
consequence, the basic parameters of the identified phenomenon include the volume
of discharge deficit in the period when it is lower than the threshold flow and the
duration of the low flow event (Fig. 12.2a).
The calculated deficits of drought streamflow were transformed into a relative
deficit (RVn), which made it possible to compare results from catchments of variable surface area [7]. The presented characteristic is calculated as per the following
formula:
RV n =
V n
V max
· 100%
(12.1)
where:
RVn relative drought streamflow deficit (%),
E. Tomaszewski and M. Kozek
drought and low flows of low groundwater levels, often without the soil drought
stage. At the next stage, groundwater resources are exhausted, and surface water
reserves need to be mobilized to mitigate the soil drought. However, by this time
the drought severity is so strong that water redistribution quickly leaps from local to
regional scale and results in low flow of rivers. As a result, when the hydrological
drought should only naturally begin, low flows of underground and surface waters
are already highly advanced.
Many regions of the world, where the effects of drought are particularly harsh or
dangerous, introduced early warning systems. They improve and implement methods
for short-term and seasonal forecasting of drought and develop an integrated information exchange system between networks. They include various scenarios of drought
development and emergency plans at the state and regional levels. The systems also
assess the risk of individual events and available insurance options [19]. Drought
risk assessment in Poland involves not only the strategies of mitigating its effects but
also the process of drought risk management [20].
12.2 Methodology and Data
River low flow, i.e. the last stage of the response to insufficient supply, is considered
a good indicator of hydrological drought [21–23]. It is usually defined as a period
of low flows (water levels) in a river or flows maintained during dry weather [14,
24]. Precise definition of the low flow depends on a specific research approach.
One of them is a threshold level method in which an analysis of a flow hydrograph
with respect to a threshold value determined based on a selected characteristic flow
enables identification of the low flows. Limit values are estimated based on second
degree main flows, periodic flows from the flow duration curve, analysis of annual
minima distribution or conventional flows adapted to specific challenges of water
management and environmental management. In this research approach, the low
flow is a period with flows lower than the established threshold flow [25–27]. As a
consequence, the basic parameters of the identified phenomenon include the volume
of discharge deficit in the period when it is lower than the threshold flow and the
duration of the low flow event (Fig. 12.2a).
The calculated deficits of drought streamflow were transformed into a relative
deficit (RVn), which made it possible to compare results from catchments of variable surface area [7]. The presented characteristic is calculated as per the following
formula:
RV n =
V n
V max
· 100%
(12.1)
where:
RVn relative drought streamflow deficit (%),