**3. Forensic analysis of droughts**

Drought is a phenomenon that has always existed, even though mankind perceives it as atypical. This perception has caused that drought has not been studied as deep as it deserves. There are still few tools to address drought issues from the perspective of decision makers [6]. Because of this, forensic analysis of droughts can have a high relevance at the present and certainly it will be even more important in the future because of incremental climate variability and the eventual climate change.

Differences in hydrometeorological variables and socioeconomic factors as well as the stochastic nature of water demands in different regions around the world have become an obstacle to having a precise definition of drought [7]. For example, a definition of drought in terms of an insufficient humidity condition caused by a deficit in precipitation over certain period of time has been proposed [8].

Forensic analysis of droughts, because of the characteristics of the natural phenomena, will help to the establishment of the beginning and the end of a certain event. Effects derived from a drought are cumulative both in time and magnitude, making it a slow process that can extend for long periods even when the moisture condition is partially recovered by precipitation. This turns the phenomenon into a very complex one.

The general methodology presented here sets the basis to address the topic by looking the establishment of theoretical elements and applications that can help in the comprehension of the causes and impacts of droughts. Forensic analysis of droughts will provide a better understanding of the phenomena on a solid base favouring the access to better information and products.

In order to carry out a forensic analysis of droughts, the following factors and variables must be at least considered:

**•** Geographical

**•** Review and adaptation of infrastructure operation policies

draining strictures

56 Forensic Analysis - From Death to Justice

**•** Development of a Flood Risk Atlas

**3. Forensic analysis of droughts**

and the eventual climate change.

period of time has been proposed [8].

turns the phenomenon into a very complex one.

**•** Projects for works and actions for flood control

**•** Development of reforestation plans, soil control projects

**•** Review of coordination plans among the different level of government.

etcetera)

**•** Review of the hydraulic capacity of cross sections of the river in bridges and of other

**•** Review of urban infrastructure vulnerability (water supply, sewage, treatment and

**•** Determination of the vulnerability of irregular human settlements in face of floods **•** Current status of natural streams and river in regard of obstructions and invasions

**•** Development of hydrologic criteria and its consideration in urban development plans

**•** Incentives for the use of measures of rainfall control in the source (in site). Best manage‐ ment practices such as the ones considered as 'sustainable urban drainage systems'.

Drought is a phenomenon that has always existed, even though mankind perceives it as atypical. This perception has caused that drought has not been studied as deep as it deserves. There are still few tools to address drought issues from the perspective of decision makers [6]. Because of this, forensic analysis of droughts can have a high relevance at the present and certainly it will be even more important in the future because of incremental climate variability

Differences in hydrometeorological variables and socioeconomic factors as well as the stochastic nature of water demands in different regions around the world have become an obstacle to having a precise definition of drought [7]. For example, a definition of drought in terms of an insufficient humidity condition caused by a deficit in precipitation over certain

Forensic analysis of droughts, because of the characteristics of the natural phenomena, will help to the establishment of the beginning and the end of a certain event. Effects derived from a drought are cumulative both in time and magnitude, making it a slow process that can extend for long periods even when the moisture condition is partially recovered by precipitation. This

The general methodology presented here sets the basis to address the topic by looking the establishment of theoretical elements and applications that can help in the comprehension of the causes and impacts of droughts. Forensic analysis of droughts will provide a better

	- **–** Hydrometeorology
	- **–** Historical climatology
	- **–** Flows and levels of surface and groundwater sources
	- **–** Extraction zones subject to prohibition
	- **–** Water availability
	- **–** Water pressure degree
	- **–** Water uses
	- **–** Water demands
	- **–** Water quality
	- **–** Infrastructure for storage, recharge, conduction, treatment and distribution of drinking water, waste water, irrigation, etc.
	- **–** Population
	- **–** Poverty and social backwardness
	- **–** Economic and productive activities
	- **–** Attention and mitigation plans and programs
	- **–** Action and development plans and programs
	- **–** Historical records regarding drought indicators
	- **–** Documentation of historical droughts (categorized)
	- **–** Paleoclimate studies if available

The general methodology recommends the fulfilment of the following processes and analysis:


scales for which a long time series is essential [7]. With this process, we look forward to establish the permanence, duration and frequency.

The general methodology recommends the fulfilment of the following processes and analysis: **•** Integration of a Geographical Information System (GIS), by the use of commercial tools or freeware. An important step is the construction of the base map. Physiographic, geomorphologic and edaphologic characteristics have to be determined. Maps of vegeta‐ tion and land use or economic activities will be of help. Information from agriculture, cattle rising, urban, etc., will contributed to the better understanding of the study area. All of these have to be integrated in the system for the study zone. The integration of the information allows the possibility to work with map algebra and other geo processes,

**•** Edaphology and vegetation analysis. With the help of the GIS, a detailed analysis on the edaphology of the study region and its vegetative covers should be carried out. Soil degradation and loss because of erosion are two important factors to consider. These topics, with special emphasis in edaphology, are not sufficiently addressed in drought

**•** The forensic approach will seek to provide indicators of the internal biologic activity of the soil, among other processes associated to water storage and the resistance to deficits. As it is well known, vegetative cover favours water retention in the basin, reducing with it, the surface runoff. This helps to aquifer recharge and the better performance of the

**•** Analysis of the status and quality of hydrometeorological records and climate in general. We seek to have flow records, surface water information and groundwater levels, rainfall, drought indices, operational policies, soil moisture and evapotranspiration. Observation, interpretation and analysis of sufficient data are of great importance for this type of studies. Basically, error or absence of a particular data may have effects on the estimates of probability of extreme events with high return periods. Before using a data set, its validity and accuracy should be verified. The accuracy is the correctness of the data, while validity refers to the applicability of the data for the purpose for which the values will be used [9]. The World Meteorological Organization recommends some techniques for data validation in its Document No. 168 [10]; for example, graphical representation of the rainfall or flow depends on the height of the water, in order to detect small bumps (or any episode of flooding) not accompanied by significant rainfall, and vice versa. The success of the analysis results and subsequent decision-making process depends on data quality.

**•** Spatial and temporal distributions: Once data have been validated, a geostatistical analysis can be performed. With this, spatial-temporal distributions can be constructed from recorded information. There are several methods to make this statistical spatial analysis, for example, inverse distance weighting, splines or even kriging [11]. Any of these techniques can be used, in order to determine the magnitude of the phenomena in space, which according to its causes, can be from local to regional. Of course, each method should consider its own restrictions. In the case of the time series analysis, it will allow characterizing the drought event in duration, both inter annual or seasonal. It should be noted that a drought variable should be able to quantify the drought for different time

making a lot easier any subsequent spatial analysis.

studies.

whole water system.

58 Forensic Analysis - From Death to Justice


**•** Water balance integration: This balance allows to quantify diverse water cycle compo‐ nents by the establishment of relationships among hydrologic variables such as water offer and demand and by considering spatial and temporal distributions. This is used to calculate the so-called 'hydric pressure', as a result of the balance between offer and demand. This balance allows the quantitative evaluations of water resources and the modifications because of human activities, both past and present. A water balance can also be used to predict the impact derived from those modifications. Drought forensic analysis is used to identify the influence of those factors on the magnitude of the event and on its frequency, that is, its return period. Water balance is based on the mass conservation principle, sometimes called continuity equation, in which in a simple manner, the variation in volume, in each period, is given by the difference between inflows and outflows of the system. This can be stated as [17]:

$$P + \mathcal{Q}\_{\mathcal{S}\_I} + \mathcal{Q}\_{U\_I} - E - \mathcal{Q}\_{\mathcal{S}\_o} - \mathcal{Q}\_{U\_o} - \Delta S - \nu = 0$$

where

*P* is the precipitation in form of rain or snow (self-basin), *QSI* and *QUI* are the surface and groundwater inflows (both from within the basin or from outside), *E* is the evaporation from the water surface, *QSO* and *QUO* are the surface and groundwater outflows (both from within the basin or from outside), *ΔS* is the storage and *v* is the residual term in the difference.

The analysis can be more or less simplified depending on the available information and the different components in the study case: water bodies such as reservoirs, lakes, rivers, creeks, etc.; hydrologic characteristics (basins, sub-basins, etc.) and the period under analysis. Computation of the components should be independent as much as possible, avoiding the 'closure' of the balance with unknown components. Once the balance is finished, a series of different scenarios can be studied.


should be taking into account. With these and the action and development plans and programs, the identification of the level of services and social exclusion can be clearly identified. All of these should be considered in relation to the infrastructure growth and development. It is clear for example that when large reservoirs exist, the impacts of short duration droughts can be hardly perceived.

**•** Water balance integration: This balance allows to quantify diverse water cycle compo‐ nents by the establishment of relationships among hydrologic variables such as water offer and demand and by considering spatial and temporal distributions. This is used to calculate the so-called 'hydric pressure', as a result of the balance between offer and demand. This balance allows the quantitative evaluations of water resources and the modifications because of human activities, both past and present. A water balance can also be used to predict the impact derived from those modifications. Drought forensic analysis is used to identify the influence of those factors on the magnitude of the event and on its frequency, that is, its return period. Water balance is based on the mass conservation principle, sometimes called continuity equation, in which in a simple manner, the variation in volume, in each period, is given by the difference between inflows

0 *I I OO PQ Q EQ Q Sv* + + - - - -D - = *SU S U*

groundwater inflows (both from within the basin or from outside), *E* is the evaporation

within the basin or from outside), *ΔS* is the storage and *v* is the residual term in the

The analysis can be more or less simplified depending on the available information and the different components in the study case: water bodies such as reservoirs, lakes, rivers, creeks, etc.; hydrologic characteristics (basins, sub-basins, etc.) and the period under analysis. Computation of the components should be independent as much as possible, avoiding the 'closure' of the balance with unknown components. Once the balance is finished, a series of

**•** Hydraulic analysis of actual Infrastructure in terms of resilience: More than just an audit, infrastructure must be revised in order to find the capacity that the region had to adapt infrastructure management and resist alterations without disturbing its functionality in a significant way. Infrastructure requires adaptation in accordance to needs of the region in order to satisfy demands. Because of this, responsible institutions or organizations must have a strategic vision plans, more preventive than reactive and corrective. In the ideal case, systems should have been designed adequately and in comply with standards and norms. Infrastructure should have been operated according to the policies established.

**•** Population and productive activities status and growth: Emphasis in this point is on classifying the study zone in terms of the main activities so the effects and impacts of drought in them can be clearly determined. By considering the differences for example between agricultural and urban sector, a more precise analysis can be performed. For all sectors considered, according to the productive activity, the social and poverty indices

and *QUI*

are the surface and groundwater outflows (both from

are the surface and

and outflows of the system. This can be stated as [17]:

*P* is the precipitation in form of rain or snow (self-basin), *QSI*

and *QUO*

where

60 Forensic Analysis - From Death to Justice

difference.

from the water surface, *QSO*

different scenarios can be studied.


help and support granted would serve as a base to determine if the application of those resources was efficient. The construction of performance indicators would be appreciated for future analysis and future use of the damages—support—effects relationship. For example, Jiménez [18] shows methodological guides for the construction of indicators, defining them as a tool that offers quantitative information with respect to achievements of results in the delivery of products or services generated by the institution, covering both quantitative and qualitative aspects. Also, historical water demand data and its relationship to drought declaratives need to be analyzed. In the forensic analysis, even paleoclimatology studies can be considered, such as tree ring studies that can offer information of long past events.

