The rapidly increasing frequency of disasters has become a menace to human habitation across the globe. Effective disaster risk reduction and management can be achieved through the deployment of geospatial data for all the phases of disaster management, including prevention, mitigation, preparedness, vulnerability reduction, response and relief
Disaster constitutes one of the greatest threats to development and socio-economic well being of the people. It retards development and is particularly hard on the poor people. The frequency and magnitude of natural and human induced disaster and emergencies are constantly becoming unpredictable and having grave consequences on present day human civilization. There are three basic phases of disaster management: Pre-disaster, during disaster and after disaster.
Surveying, mapping and GIS techniques are now used to facilitate disaster management through the production of model for visualisation of the effect of disaster, to mitigate, effectively deploy rescue team and undertake post disaster reconstruction and rehabilitation. The National Capacity Assessment Report indicates that Nigeria is very prone to flooding, mainly along the Niger River through Benue and Sokoto basin and this affected agricultural land use and inhabitants to a great extent. Many of the country's larger rivers have flood plains which are subjected to flooding during the rainy season, largely due to poor environmental management.
NEMA (National Emergency Management Agency) has been actively involved in Disaster Risk Reduction (DRR) through inclusive cooperation, sharing of experience and capacity building with emphasis on disaster prevention, mitigation, preparedness, vulnerability reduction, response and relief. The expected outcome of these initiatives will be more effective with the appropriate deployment of geospatial data in the right quantity, quality and format.
There are several phases and stages involved in disaster management cycle. However, there are no standardised rules defining the different phases of the disaster management cycle. Different agencies use different cycles depending upon their objectives. However, while approaches vary, it is agreed that disaster management activities should be carried out in a cycle. In disaster management, there are six (6) major aspects viz: preparedness, prevention, mitigation, Risk reduction, recovery and response.
It will be a difficult task, if not impossible, to attempt to prevent disasters of whatever type, nature or magnitude in an environment that is not well understood in all facets. Medium scale topographical map of the area of interest, depicting all the terrain, relief features, drainages, hydrography, communities and settlements is one of the required spatial data that will inform and guide decisions for any disaster preventive intervention. It is the map that will present the environment as it is and assist in determining settlements or communities that are susceptible to flooding. The maps will also provide a platform for preparing evacuation plan and environmental planning. The process of setting or designing standards and buffer zone within which there must not be any permanent structures, is achieved by maps and other geo-information. Designing drainages and other channels that will drain excess water for disaster prevention is not possible without accurate maps.
In the process of preparedness, it is obvious that geospatial data in the form of base map or environmental sensitivity Index map of the area in question is a must, to know the area that is vulnerable to the impending disaster; the location of facilities in the area; easy access to the area in time of crisis and possible area to relocate people.
Considerable losses of life and property could be avoided through better information about the risk and onset of disasters, improved risk assessment, planning and disaster monitoring. All the activities mentioned here will require geo-information for their implementation. Disaster mitigation measures may be structural (e.g. flood dikes) or non-structural (e.g. land use zoning). Mitigation activities incorporate the measurement and assessment of the evolving risk environment. Activities may include the creation of comprehensive, pro-active tools that help decide where to focus funding and efforts in risk reduction.
Making adequate preparation to reduce the impact of disaster will require identifying areas that will be affected in case of disaster; this will require environmental monitoring, mapping and other mitigation measures which include hazard mapping, adoption and enforcement of land use and zoning practices, implementing and enforcing building codes, flood plain mapping, reinforced tornado safe rooms, burying of electrical cables to prevent ice build-up, raising of homes in flood-prone areas and disaster mitigation public awareness programs.
In a disaster situation, after an earthquake or during a flood, geospatial data can be the determining factor in answering pressing questions such as: Which roads are still accessible, which houses are damaged, where could a helicopter land? and so on.
Recovery, post disaster reconstruction and rehabilitation
Recovery activities include rebuilding infrastructures, health care and rehabilitation. These should blend with development activities, such as building human resources for health and developing policies and practices to avoid similar situations in future. Again the place of geospatial data such as base map, topographic map and Digital Elevation Model (DEM) in reconstruction and rehabilitation processes after disaster is very critical as it will provide information for design and sustainable planning.
The aspect of disaster management that are carried out before disaster entails maintenance of high level of preparedness, capacity building including training of volunteers, definition of standard operational procedure for disaster response sourcing and collaboration with disaster relief partners and other stakeholder in disaster management. During disaster, the major activity is prompt response, having an overview of the extent and the spreading of the disaster and finding the access possibility to extend relief. Part of the activities also involves reaching out as soon as possible to other relief partners for support. While disaster management after disaster has to do with recovery, reconstruction and rehabilitation, it also involves reviewing of the work done and taking corrective measures, prepared audited accounts, reports and update the procedure for future use.
Vulnerability and risk reduction
It is not possible to make wise management of land and the environment and make good choices about where we site our facilities in order to reduce the chances of disaster without a model of the environment in terms of maps and other geo-information.
Geospatial data in disaster management cycle
Geospatial Data plays a big role in disaster management. Features impacted by disasters are geographically located and have geographic addresses. Geospatial data constitutes the disaster management information cell for all phases of disaster management through preparedness, damage assessment and relief planning.
Geospatial data will provide information about the areas that are susceptible to flood and locations that people and live stock can be evacuated to incase of a disaster. An Environmental Sensitivity Index (ESI) Map will provide information about possible safe access to an environment and location of other relief facilities and infrastructures in the event of disaster. It serves as decision making tool as well as a compass for relief teams.
GIS and remote sensing are reliable tools that have been used in the evaluation of geo-environmental catastrophes by providing a sort of synoptic coverage of a very broad area in a cost effective way, which overcomes the bottle-necks and limitations caused by the conventional ground stations in recording hydrological information during an extreme event. Moreover, remote sensing tools provide the researcher with multi-date satellite imageries, which in turn aids the researcher in monitoring and recording the change progress of the past flood events. In recent years, development in the areas of GIS and remote sensing has been embedded into the assessment of geo-environmental catastrophes, which profoundly facilitated advancement of flood susceptibility mapping, flood risk assessment, and erosion control. It is evident that flood related problems could be solved through planning, studies and also through detailed mapping of flood plains. GIS systems are built to cover a wide range of applications and are designed to integrate a vast variety of environmental data, allowing them to work together in a readily accessible way.
Management of flood
Flood risk management includes both the chance of an event taking place and its potential impact. Land use planning informed by floodplain management plans can reduce risk for new development areas. Flood risk is harder to manage in existing developed areas; however modification measures such as dams or levees can change the behavior of floodwaters. Similarly, property modification measures can protect against harm caused by floods to individual buildings, and response modification measures help communities deal with floods and enforcement of building regulations in the urban can considerably reduce disaster risks.
However, all these modifications cannot be properly and practically implemented without adequate information being provided about the environment. For holistic environmental information to be available for the management of flood disaster in Nigeria there should be synergy among all stakeholder in environmental information acquisition, manipulation, processing, analysing and predictions. Some of this vital information is essentially geospatial data.
With the advent of digital and space technology, the surveyor now provides intelligent digital maps and models that could help the National Emergency Management Agency (NEMA) in mitigating natural disasters, especially floods. These maps/information ranges from flood plains maps, watershed, stream network, flow direction, sink/fill and flow accumulation information which would be used to model the environment.
With the application of GIS and Remote Sensing the surveyor could model and analyse the data and come up with useful information such as; component of drainage basin and watershed and flood plain model of the environment.
Rapid mapping for pre and post disaster needs assessment (PDNA)
The flood that ravaged Nigeria in 2012 had greater effects in communities along the major rivers in the country that is, river Benue, Niger and its numerous tributaries. This is due to many reasons principally from climate change effects and the release of water from Lagdo dam in the Cameroun and further compounded by other reasons ranging from lack of awareness to poor drainage system.
In order to assess the flood disaster, in extent and coverage and ascertain the level of damage in the environment and the number of communities affected by the flood, Rapid Mapping of the affected area was carried out by National Emergency Management Agency (NEMA) in Collaboration with the Office of the Surveyor General of the Federation (OSGoF) and National Space and Research Development Agency (NASRDA). This Mapping technique was effective for provision of information for rehabilitation; mitigate and prepare against future occurrence.
The total number of States involved in the project was seventeen, which included: Adamawa, Akwa Ibom, Bayelsa, Benue, Cross River, Delta, Edo, Imo, Jigawa, Kebbi, Kogi, Kwara, Nassarawa, Niger, Plateau, Rivers and Taraba States. The estimated cost of the damage was conservatively put at N2.6Tn by NEMA.
CORS Stations for rainfall prediction
There are different methods of weather forecast, which are, by Interactive Analysis of Radar and Satellite Imagery; By Statistical Inferences; Indigenous approach to weather forecast and by Surveying and Mapping technique of GNSS Meteorology, which is Continuously Operating Reference Stations for rainfall predictions.
In Nigeria, the prediction model is based on the strong tele-connection between El Nino/Southern Oscillation (ENSO), Sea Surface Temperature (SST) anomalies and rain-bearing weather system over Nigeria. ENSO is a recurrent abnormal shift in winds and ocean currents centered in the south Pacific region that produces extreme weather and climate conditions in many parts of the world. The model also incorporates phonological and soil information as well as historical daily weather data from 39-meteorological stations spatially distributed over Nigeria for 22 ENSO. However, there are real problems in the national weather forecast and rainfall predictions because there are fewer upper air observations in Nigeria. Thus, most of the present predictions and forecasting models are mere empirical statistical extrapolations. The rainfall prediction from CORS will complement the present effort of NIMET.
Nigerian GNSS reference network
The establishment of NIGNET is an additional tool for monitoring one of the most important meteorological and climate parameters: the quantity of Precipitable Water Vapor (PWV) in the atmosphere, which is directly correlated with the precipitation. Precipitable Water Vapor plays a major role in many atmospheric processes concerning physics, thermodynamics and dynamics. The knowledge of the spatial and temporal distribution of Water Vapor in the lower troposphere is essential for both accurate quantitative prediction of precipitation and better understanding of convective processes. The atmospheric water vapor is particularly important in clouds formation and composition, convective initiation and feeding and also precipitation processes.
Currently, there are 15 stations on the distribution of the NIGNET network. Eleven of those were installed by OSGOF and four were installed by Presidential Land Reform Committee. OSGOF also collaborates with Regional Centre for Training in Aerospace Surveys (RECTAS) on the data maintenance of RECTAS station at Ife. The data from the permanent stations are collected at the headquarters in Abuja.
GNSS and water vapor
In recent years, the use of GNSS observations to sense the Precipitable Water Vapor (PWV) in the troposphere has increased significantly. GNSS has large advantages since it is a system that works in all weather conditions, with continuous unattended operation and good time resolution.
The basic principle is, while travelling through the Earth’s atmosphere the GNSS signal experiences delays caused by the atmosphere, mainly the ionosphere and troposphere. Considering the dispersive character of the ionosphere for the GNSS frequencies, ionospheric effects are minimized using a fitted linear combination of the GNSS frequencies. Conversely, the tropospheric effects are not frequency dependent below 15 GHz. The main effect of the troposphere on GNSS positioning is an extra delay of the radio signal emitted by GNSS satellites. This delay is time varying, due to the variables pressure, temperature and water vapor content of the atmosphere and cannot be modeled or predicted with sufficient precision for high precision positioning, especially in real-time. To model out the perturbation, a set of tropospheric parameters is estimated during the GNSS data analysis: Zenith delays, and more recently, horizontal gradients. The correlation between these delays and the state of the atmosphere makes the GNSS an efficient tool for meteorological observation.
OSGoF products for disaster risk reduction
The Office of the Surveyor General of the Federation has produced overtime the under listed products and services:
- Digital and update Topographical Maps at various scales
- Digital and updated Road map of the country
- 10m digital Elevation Model of the entire country
- Horizontal and Vertical Geodetic Control network at various order of accuracies.
- Tidal information to aid construction of bridges.
- Provision of Continuously Operating reference Stations (CORS) Data for all Global Navigation Satellite System (GNSS) applications including structural deformation monitoring.
AFREF technology at OSGoF
The Office of the Surveyor General of the Federation (OSGoF) has the capability to handle consultancy and technical support services to all agencies that make use of geospatial information. Presently monitoring of infrastructures is made possible by the installation and maintenance of fifteen CORS in line with the African Geodetic Reference Frame (AFREF) guidelines within Nigeria and training of staff on how to effectively use them. These stations are geometrically located to cover the entire country as shown in fig below
It is apparent that disaster risk reduction and management is a multi-sectoral area. It is equally clear that, in all the phases of disaster management; before, during or after, the role of geospatial data is key to effective disaster management. One of the recommendations of UN-SPIDER for improve collaboration and cooperation among the stakeholders in disaster management is quite appropriate, as this will create a platform for the required synergy to be generated for more effective policy and action for disaster management. It will also facilitate interoperability and effective data sharing among the stakeholders in disaster management.