**Table 4.**

*Summary statistics.*

*Analysis of Non-Rainfall Periods and Their Impacts on the Soil Water Regime DOI: http://dx.doi.org/10.5772/intechopen.82399*

#### **Table 5.**

*Hydrology - The Science of Water*

depended on the depth to which the soil water storage was monitored in field. The results of the simulation and the measurements are shown in **Figure 6**. The diagram shows a very high concordance between the calculated and the measured values which is proven by the results in **Figure 7**. It is a quantile-quantile plot which shows the linear trend and the correlation coefficient between the measured and the modelled values. The R-squared statistic indicates that the model as fitted explains 86.37% of the variability in measurement. The correlation coefficient equals 0.93, indicating a relatively strong relationship between the variables. Other basic charac-

The results show that, especially in terms of moisture, the model GLOBAL θ > TP tends to overestimate the real state. When the moisture is lower, it tends to underestimate it. In addition, the t-test was applied to compare the mean values and the F-test to compare the standard deviations of the measured and the modelled values. The results of the tests are shown in **Table 5**. The tests showed that the null hypothesis regarding the equality of the mean values and standard deviations of

**Statistics Measurement Simulation** Count 22 22 Average 202.12 204.43 Standard deviation 37.89 47.84 Variance 1435.57 2288.79 Coefficient of variation 18.75% 23.40% Minimum 153.32 157.09 Maximum 287.38 303.43 Range 134.07 146.34 Standard skewness 1.455 1.877 Standard kurtosis −0.284 −0.584

*Representation of the linear dependence via the correlation coefficients between the measured and the modelled*

*daily values of integral soil water content to the depth of 0.8 m in Milhostov.*

teristics of the descriptive statistics are listed in **Table 4**.

**76**

**Table 4.** *Summary statistics.*

**Figure 7.**

*Results of the t-test and F-test.*

the measured and simulated values cannot be rejected. The results indicate that the model is suitable for the examined area and it can be used for the simulation of the water regime in the unsaturated soil zone. It should be noted that the model has been verified and successfully applied in other areas around Slovakia (Novák et al., 1998).

**Figure 8** shows the contour lines representing the volume moisture and it was made based on the moisture values monitored up to the depth of 0.8 m by 0.10 m thick layers in Milhostov during the growing season of 2007. The picture shows that the whole profile was dry to the subsoil layers.

#### **3.3 Results of numerical simulation**

**Table 6** lists the basic characteristics of the descriptive statistics applied to the following: seasonal, monthly and daily totals of ET0, D, P; average soil water storage during the growing season to the depth of 1.0 m and the mean location of GWL under the surface during the growing season. **Table 6** shows that the longterm mean evaporation during the growing season in the form of ETa is 315.17 mm (59.4% of ET0) while evaporation ET0 is 530.63 mm. This leads to the long-term evaporation deficiency of 215.45 mm, which is 40.6% of ET0. Long-term mean rainfall total during the growing season is 70.0% (371.44 mm) of ET0. Long-term mean

**Figure 8.** *Contour lines of the volumetric moisture up to 0.80 m during the growing season of 2007.*

*Hydrology - The Science of Water*

**Table 6.**

**79**

**Figure 9.**

*Long-term mean monthly totals of ET0, ETa and D.*

*Analysis of Non-Rainfall Periods and Their Impacts on the Soil Water Regime*

a is 88.44 mm. Long-term mean daily total of ET

0 is 2.91 mm. Mean depth of the GWL under the surface is 135.09 cm. **Table 6** shows statistical characteristics of the seasonal, monthly and daily totals of

D. The results indicate that the highest long-term mean monthly total of evapora

profile contains enough water. From June until the end of the growing season ET

age to the depth of 1 m (WS), mean temperatures (T) and mean GWL during the

It is obvious that during the examined period, the difference between ET

a raised. Evaporation deficiency 'D' therefore increases. Variability has also grown during the last 15 years. As for standard deviation 'D', from 1970 to 1985 it was 63 mm, from 1986 to 2000 it was 69 mm and during 2001–2015 it reached 158 mm. The variability has raised in all examined parameters during the last 15 years (e.g. WS raised by 50%). With the exception of evaporation, the trends are

**Table 7** correlates the examined parameters. The most significant and clos

est relation is between soil water storage and D (**Figure 11**) and GWL which are inversely proportional. On the other hand, water storage in the root zone of a soil

a . The processes can be explained by the fact that GWL is a lower boundary of the unsaturated soil zone and for the purpose of soil water regime, it is defined as the lower boundary condition. The lower boundary of the unsaturated soil zone is thus dynamic and, depending on the interaction with the groundwater, it can change in space and time. When GWL is high, groundwater can reach the soil profile. In depressed lowland areas, such as ESL, groundwater often reaches the surface of the ground and the unsaturated soil zone is lost. Due to its fluctuation

tion deficiency is in July and August. It is caused by the fact that the mean monthly soil water storage gradually diminishes during the growing season until July when it

a, D, P; mean soil water storage during the growing season to the depth of 1.0 m and mean location of the GWL under the surface during the growing season. **Figure 9** shows the long-term mean values of the monthly total of ET

0, ET

a is 1.73 mm

0, ET

a increases and reaches the top value

a, P totals, mean soil water stor

a occurs in June when soil

a and

a

0 and

*DOI: http://dx.doi.org/10.5772/intechopen.82399*

stops at the minimum value. To the contrary, ET

**Figure 10** shows the development of D, ET

growing seasons between 1970 and 2015.

profile statistically depends on GWL and ET

in July. The maximum value of long-term mean total of ET

monthly total of ET

continuously drops.

while ET

ET 0, ET

ET

balanced.

*Statistical characteristics of the seasonal, monthly and daily totals of ET0, ETa, D, WS, P and GWL.*

#### *Analysis of Non-Rainfall Periods and Their Impacts on the Soil Water Regime DOI: http://dx.doi.org/10.5772/intechopen.82399*

monthly total of ETa is 88.44 mm. Long-term mean daily total of ETa is 1.73 mm while ET0 is 2.91 mm. Mean depth of the GWL under the surface is 135.09 cm. **Table 6** shows statistical characteristics of the seasonal, monthly and daily totals of ET0, ETa, D, P; mean soil water storage during the growing season to the depth of 1.0 m and mean location of the GWL under the surface during the growing season.

**Figure 9** shows the long-term mean values of the monthly total of ET0, ETa and D. The results indicate that the highest long-term mean monthly total of evaporation deficiency is in July and August. It is caused by the fact that the mean monthly soil water storage gradually diminishes during the growing season until July when it stops at the minimum value. To the contrary, ETa increases and reaches the top value in July. The maximum value of long-term mean total of ETa occurs in June when soil profile contains enough water. From June until the end of the growing season ETa continuously drops.

**Figure 10** shows the development of D, ET0, ETa, P totals, mean soil water storage to the depth of 1 m (WS), mean temperatures (T) and mean GWL during the growing seasons between 1970 and 2015.

It is obvious that during the examined period, the difference between ET0 and ETa raised. Evaporation deficiency 'D' therefore increases. Variability has also grown during the last 15 years. As for standard deviation 'D', from 1970 to 1985 it was 63 mm, from 1986 to 2000 it was 69 mm and during 2001–2015 it reached 158 mm. The variability has raised in all examined parameters during the last 15 years (e.g. WS raised by 50%). With the exception of evaporation, the trends are balanced.

**Table 7** correlates the examined parameters. The most significant and closest relation is between soil water storage and D (**Figure 11**) and GWL which are inversely proportional. On the other hand, water storage in the root zone of a soil profile statistically depends on GWL and ETa.

The processes can be explained by the fact that GWL is a lower boundary of the unsaturated soil zone and for the purpose of soil water regime, it is defined as the lower boundary condition. The lower boundary of the unsaturated soil zone is thus dynamic and, depending on the interaction with the groundwater, it can change in space and time. When GWL is high, groundwater can reach the soil profile. In depressed lowland areas, such as ESL, groundwater often reaches the surface of the ground and the unsaturated soil zone is lost. Due to its fluctuation

**Figure 9.** *Long-term mean monthly totals of ET0, ETa and D.*

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**Day**

**Month**

**78**

**Statistic**

Mean St. er. Median

St. dev.

S. var. Kurtosis

Skew. Range

Min Max Count

**Table 6.**

530.6

12.0 533.5

81.1 6580.3

0.5 −0.2 409.9 302.7 712.6

46

46 *Statistical characteristics of the seasonal, monthly and daily totals of ET0, ETa, D, WS, P and GWL.*

46

46

46

46

282

282

8235

8235

526.2

556.6

400.6

671.2

220.7

160.2

124.5

9.3

6.0

156.1

0.2

213.6

226.8

61.1

28.3

3.3

0.0

0.0

370.2

556.4

187.0

444.4

159.6

131.9

121.3

9.3

6.0

0.7

0.8

0.9

0.93

0.2

0.3

0.5

0.3

0.6

0.1

1.3

1.2

2.03

3.8

−0.3

0.5

0.1

0.3

6316.8

11958.3

1384.9

7373.9

580.3

631.8

477.5

1.9

1.1

79.5

109.4

37.2

85.9

24.1

25.1

21.9

1.4

1.1

290.7

209.0

270.2

360.9

136.2

87.3

51.1

2.8

1.6

11.7

16.1

5.5

12.7

3.6

1.5

1.3

0.0

0.0

315.2

215.5

278.4

371.4

135.1

88.4

52.5

2.9

1.7

**ET0**

**ETa**

**D** **[mm]**

**WS**

**P**

**GWL**

**[cm]**

**[mm]**

**[mm]**

**ET0**

**ETa**

**ET0**

**ETa**

**VO**

#### **Figure 10.**

*Evapotranspiration deficiency and the water regime elements during the growing seasons 1970–2015.*

in time, groundwater can reach the soil profile even when the average GWL is lower. In this way, the interaction processes influence on the soil water storage and its availability for the plant cover. It is especially observable during periods of meteorological drought. During longer periods with no rainfall, precipitation cannot cover the actual evapotranspiration ETa and the drying process begins. There is a slight retardation in time in terms of the impact of the drying process on GWL and the unsaturated soil zone. In lowland areas, first layers to be dried are the upper layers of a soil profile. Drying then spreads to the lower layers towards GWL. Time retardation lies in that groundwater supplies the

**81**

**Figure 12.**

*Analysis of Non-Rainfall Periods and Their Impacts on the Soil Water Regime*

**ETa [mm]**

**T [°C]** **GWL [cm]**

**WS [mm]**

**D [mm]**

**ET0 [mm]**

T [°C] −0.2 0.6 0.0 1.0

*temperatures, GWL—groundwater level, WS—water storage, D—evaporation.*

GWL [cm] 0.6 −0.3 0.8 −0.2 1.0

WS [mm] 0.6 −0.2 0.9 −0.1 0.9 1.0

D [mm] −0.7 0.7 −0.7 0.4 −0.8 −0.8 1.0 *P—precipitation, ET0—potential evapotranspiration, ETa—actual evapotranspiration deficiency, T—mean*

unsaturated soil zone with water and thus ameliorates its availability for the root zone of the plant cover. In consequence, GWL drops and the unsaturated soil zone becomes thicker. When GWL drops under the critical (threshold) point,

*Growing seasons 1970–2015 ordered by soil water storage in a soil profile to the depth of 1 m.*

*Graphical representation of the exponential dependence between evapotranspiration deficiency (D) and water*

*DOI: http://dx.doi.org/10.5772/intechopen.82399*

**[mm]**

ETa [mm] 0.6 0.1 1.0

ET0 [mm] −0.3 1.0

*Correlation table of the examined parameters.*

*storage (WS) in soil to the depth of 1 m; R = 0.8.*

**Parameters P**

P [mm] 1.0

**Table 7.**

**Figure 11.**

*Analysis of Non-Rainfall Periods and Their Impacts on the Soil Water Regime DOI: http://dx.doi.org/10.5772/intechopen.82399*

*P—precipitation, ET0—potential evapotranspiration, ETa—actual evapotranspiration deficiency, T—mean temperatures, GWL—groundwater level, WS—water storage, D—evaporation.*

#### **Table 7.**

*Hydrology - The Science of Water*

**80**

**Figure 10.**

*Evapotranspiration deficiency and the water regime elements during the growing seasons 1970–2015.*

in time, groundwater can reach the soil profile even when the average GWL is lower. In this way, the interaction processes influence on the soil water storage and its availability for the plant cover. It is especially observable during periods of meteorological drought. During longer periods with no rainfall, precipitation cannot cover the actual evapotranspiration ETa and the drying process begins. There is a slight retardation in time in terms of the impact of the drying process on GWL and the unsaturated soil zone. In lowland areas, first layers to be dried are the upper layers of a soil profile. Drying then spreads to the lower layers towards GWL. Time retardation lies in that groundwater supplies the

*Correlation table of the examined parameters.*

**Figure 11.**

*Graphical representation of the exponential dependence between evapotranspiration deficiency (D) and water storage (WS) in soil to the depth of 1 m; R = 0.8.*

#### **Figure 12.**

*Growing seasons 1970–2015 ordered by soil water storage in a soil profile to the depth of 1 m.*

unsaturated soil zone with water and thus ameliorates its availability for the root zone of the plant cover. In consequence, GWL drops and the unsaturated soil zone becomes thicker. When GWL drops under the critical (threshold) point,

#### **Figure 13.**

*Evapotranspiration deficiency and water regime elements in the extremely dry year of 2015.*

water transfer from GWL to the root zone ceases. Moisture conditions in the balanced layer of the root zone depend solely on rainfall and evaporation. When there is the longer period with no rainfall, water supply towards the roots stops. The upper soil horizons and subsequently the whole root zone get into the state of drought. In **Figure 12** the examined years are ordered by mean soil water storage to the depth of 1 m during the growing season.

**83**

*Analysis of Non-Rainfall Periods and Their Impacts on the Soil Water Regime*

shows the development and correlation between ET0, ETa and D.

The scheme shows that the driest year in terms of soil water storage during a growing season was the year 2015. In consequence, water regime elements in 2015 were analysed. The results of the analysis were calculated with 1-day step and they are shown in **Figure 13**. Evaporation deficiency 'D' is 257% of the long-term mean (1971–2015). ET0 is 134% and ETa is 49% of the corresponding long-term mean. The mean temperature is relatively stable, 110% of the corresponding long-term mean. Rainfall 'P' formed 61% of the corresponding longterm mean and water storage in soil to the depth of 1 m 'WS' were 77% of the corresponding long-term mean. The results shown in **Figure 13** indicate that in the other half of the growing season soil water storage dropped under the point

This corresponds to the fact that the value of 'D' was high above the average. Groundwater continuously drops during the whole growing season. **Figure 13** also

Precipitation amount and temporal distribution of the rainfall is important

The study analysed the development of ET0, ETa, D, WS, P, GWL location and T during the growing seasons during the years 1970–2015 on the basis of the measured data and the data gained via numerical simulation. The interaction processes in the root zone of a soil profile during the creation of soil water regime were quantified. The quantification is crucial for understanding the processes occurring during drought creation, duration and termination. It has been demonstrated that soil water storage depends heavily on evaporation, i.e. actual evapotranspiration ETa. Subsequently, actual evapotranspiration influences on evapotranspiration deficiency 'D' and on the location of GWL. For that reason, evapotranspiration deficiency 'D' can be considered an indicator of the drying of a soil profile. Drying starts when water inflow towards plant roots is reduced. During the state of evapotranspiration deficiency, groundwater supplies the root zone of a soil profile with water. When

for water refilling of the environment for balanced periods. Drying of soil profile occurs during long rainless periods. Meteorological drought and subsequently soil drought occurs in the case of the sufficiently long rainless period. Therefore it is necessary to know size and statistical characteristics of rainless periods (RLP). The aim of the contribution is to identify important rainless periods, quantify temporal lengths, probability characteristics and trends of RLP. Climatic station of Milhostov (N 48°39,786′; E 21°43,298′) was chosen for selection of statistically important rainless periods. Station represents wider area of lowland. Daily precipitation amounts of the 1961–2015 period was examined for the station. 20,080 daily precipitation amounts (including zero) were analysed for the period. Length of RLP was identified in two ways. Periods with zero daily precipitation amounts were considered in first selection (s0). Daily precipitation amounts lower than 2 mm were considered as zero in second selection (s2). The absolutely longest continuous period without rainfall for s0 selection (year, VP) had 35 days and occurred between 25.9.1962 and 29.10.1962. Maximal continuous rainless event extends to 53 days in case of s2 selection for the vegetal period. This event occurred in time interval 19.7.1967–9.9.1967. Number of rainy and rainless days is for individual years and their vegetal periods balanced in the long term view. Only duration of rainless events of non-vegetal periods changes in examined periods. Growth of time length of rainless days duration was identi-

*DOI: http://dx.doi.org/10.5772/intechopen.82399*

of decreased availability.

fied in non-vegetal half-year.

**4. Conclusions**

*Analysis of Non-Rainfall Periods and Their Impacts on the Soil Water Regime DOI: http://dx.doi.org/10.5772/intechopen.82399*

The scheme shows that the driest year in terms of soil water storage during a growing season was the year 2015. In consequence, water regime elements in 2015 were analysed. The results of the analysis were calculated with 1-day step and they are shown in **Figure 13**. Evaporation deficiency 'D' is 257% of the long-term mean (1971–2015). ET0 is 134% and ETa is 49% of the corresponding long-term mean. The mean temperature is relatively stable, 110% of the corresponding long-term mean. Rainfall 'P' formed 61% of the corresponding longterm mean and water storage in soil to the depth of 1 m 'WS' were 77% of the corresponding long-term mean. The results shown in **Figure 13** indicate that in the other half of the growing season soil water storage dropped under the point of decreased availability.

This corresponds to the fact that the value of 'D' was high above the average. Groundwater continuously drops during the whole growing season. **Figure 13** also shows the development and correlation between ET0, ETa and D.

### **4. Conclusions**

*Hydrology - The Science of Water*

**82**

**Figure 13.**

water transfer from GWL to the root zone ceases. Moisture conditions in the balanced layer of the root zone depend solely on rainfall and evaporation. When there is the longer period with no rainfall, water supply towards the roots stops. The upper soil horizons and subsequently the whole root zone get into the state of drought. In **Figure 12** the examined years are ordered by mean soil water stor-

*Evapotranspiration deficiency and water regime elements in the extremely dry year of 2015.*

age to the depth of 1 m during the growing season.

Precipitation amount and temporal distribution of the rainfall is important for water refilling of the environment for balanced periods. Drying of soil profile occurs during long rainless periods. Meteorological drought and subsequently soil drought occurs in the case of the sufficiently long rainless period. Therefore it is necessary to know size and statistical characteristics of rainless periods (RLP). The aim of the contribution is to identify important rainless periods, quantify temporal lengths, probability characteristics and trends of RLP. Climatic station of Milhostov (N 48°39,786′; E 21°43,298′) was chosen for selection of statistically important rainless periods. Station represents wider area of lowland. Daily precipitation amounts of the 1961–2015 period was examined for the station. 20,080 daily precipitation amounts (including zero) were analysed for the period. Length of RLP was identified in two ways. Periods with zero daily precipitation amounts were considered in first selection (s0). Daily precipitation amounts lower than 2 mm were considered as zero in second selection (s2). The absolutely longest continuous period without rainfall for s0 selection (year, VP) had 35 days and occurred between 25.9.1962 and 29.10.1962. Maximal continuous rainless event extends to 53 days in case of s2 selection for the vegetal period. This event occurred in time interval 19.7.1967–9.9.1967. Number of rainy and rainless days is for individual years and their vegetal periods balanced in the long term view. Only duration of rainless events of non-vegetal periods changes in examined periods. Growth of time length of rainless days duration was identified in non-vegetal half-year.

The study analysed the development of ET0, ETa, D, WS, P, GWL location and T during the growing seasons during the years 1970–2015 on the basis of the measured data and the data gained via numerical simulation. The interaction processes in the root zone of a soil profile during the creation of soil water regime were quantified. The quantification is crucial for understanding the processes occurring during drought creation, duration and termination. It has been demonstrated that soil water storage depends heavily on evaporation, i.e. actual evapotranspiration ETa. Subsequently, actual evapotranspiration influences on evapotranspiration deficiency 'D' and on the location of GWL. For that reason, evapotranspiration deficiency 'D' can be considered an indicator of the drying of a soil profile. Drying starts when water inflow towards plant roots is reduced. During the state of evapotranspiration deficiency, groundwater supplies the root zone of a soil profile with water. When

there is the long period with no rainfall, water transfer from GWL towards plant roots ceases. Moisture conditions in the balanced layer of the root zone depend solely on rainfall and evaporation. The processes are demonstrated on the driest growing season of 2015. From the point of view of soil water storage to the depth of 1 m this season was absolutely driest growing season in the examined period from 1970 to 2015.