Drought. Definitions. Causes. Types.

Drought occurs when there is less water available than what is normally expected in a particular location and season. It can last for days, months or years, and has severe impacts on ecosystems, agriculture and the economy. Droughts are becoming more severe and unpredictable due to climate change. There are three kinds of drought effects: environmental, economic and social. Environmental effects include the drying of wetlands, more and larger wildfires, and loss of biodiversity. Economic consequences include disruption of water supplies, lower agricultural outputs and higher food-production costs. Social and health costs include negative impacts on health, stress from failed harvests and water scarcity. Prolonged droughts have caused mass migrations and humanitarian crises. Some plant species have adapted to tolerate drought, but most arid ecosystems have inherently low productivity. The most prolonged drought in recorded history continues in the Atacama Desert in Chile. Humans have historically viewed droughts as disasters and have attributed them to natural or supernatural forces.

Definition

IPCC defines drought as "drier than normal conditions"

National Integrated Drought Information System defines drought as "a deficiency of precipitation over an extended period of time (usually a season or more), resulting in a water shortage"

National Weather Service office of the NOAA defines drought as "a deficiency of moisture that results in adverse impacts on people, animals, or vegetation over a sizeable area"

Drought is a complex phenomenon related to the absence of water, which is difficult to monitor and define.

Over 150 definitions of "drought" were published by the early 1980s, reflecting differences in regions, needs, and disciplinary approaches.

Types

There are three categories of drought: meteorological, hydrological, and agricultural or ecological drought.

Meteorological drought occurs due to lack of precipitation.

Hydrological drought is related to low runoff, streamflow, and reservoir storage.

Agricultural or ecological drought causes plant stress from a combination of evaporation and low soil moisture.

Socioeconomic drought occurs when the demand for an economic good exceeds supply due to a weather-related shortfall in water supply.

Meteorological drought usually precedes the other kinds of drought.

Hydrological drought tends to show up more slowly because it involves stored water that is used but not replenished.

Agricultural or ecological droughts affect crop production or ecosystems in general.

Agricultural drought can be caused by increased irrigation or poorly planned agricultural endeavors leading to soil conditions and erosion.

Causes

Precipitation mechanisms include convective, stratiform, and orographic rainfall, and precipitation can be categorized into three types.

Droughts mainly occur in areas with already low rainfall levels and can be triggered by high levels of reflected sunlight, continental winds, and high pressure systems.

The dry season in the tropics increases the occurrence of droughts, and bushfires are common due to the lack of water in the plants.

El Niño and La Niña events can exacerbate drought conditions in various regions around the world.

Climate change is expected to cause droughts with a significant impact on agriculture, increase the frequency of extreme events, and worsen compound warm-season droughts in Europe.

Comments

History of GIS

1. 1832 - Early Spatial Analysis in Epidemiology: - Charles Picquet creates a map in Paris detailing cholera deaths per 1,000 inhabitants. - Utilizes halftone color gradients for visual representation. 2. 1854 - John Snow's Cholera Outbreak Analysis: - Epidemiologist John Snow identifies cholera outbreak source in London using spatial analysis. - Maps casualties' residences and nearby water sources to pinpoint the outbreak's origin. 3. Early 20th Century - Photozincography and Layered Mapping: - Photozincography development allows maps to be split into layers for vegetation, water, etc. - Introduction of layers, later a key feature in GIS, for separate printing plates. 4. Mid-20th Century - Computer Facilitation of Cartography: - Waldo Tobler's 1959 publication details using computers for cartography. - Computer hardware development, driven by nuclear weapon research, leads to broader mapping applications by early 1960s. 5. 1960 - Canada Geograph...

Platforms in Remote Sensing

In remote sensing, a platform is the physical structure or vehicle that carries a sensor (camera, scanner, radar, etc.) to observe and collect information about the Earth's surface. Platforms are classified mainly by their altitude and mobility : Ground-Based Platforms Definition : Sensors mounted on the Earth's surface or very close to it. Examples : Tripods, towers, ground vehicles, handheld instruments. Applications : Calibration and validation of satellite data Detailed local studies (e.g., soil properties, vegetation health, air quality) Strength : High spatial detail but limited coverage. Airborne Platforms Definition : Sensors carried by aircraft, balloons, or drones (UAVs). Altitude : A few hundred meters to ~20 km. Examples : Airplanes with multispectral scanners UAVs with high-resolution cameras or LiDAR High-altitude balloons (stratospheric platforms) Applications : Local-to-regional mapping ...

Spectral Signature vs. Spectral Reflectance Curve

Spectral Signature A spectral signature is the unique pattern in which an object: absorbs energy reflects energy emits energy across different wavelengths of the electromagnetic spectrum. ✔ Key Points Every natural and man-made object on Earth interacts with sunlight differently. These interactions produce a distinct pattern , just like a "fingerprint". Sensors on satellites record these patterns as digital numbers (DN values) . These patterns help to identify and differentiate objects such as vegetation, soil, water, snow, buildings, minerals, etc. ✔ Examples of Spectral Signatures Healthy vegetation → High reflectance in NIR , strong absorption in red Water → Strong absorption in NIR and SWIR , low reflectance Dry soil → Gradual increase in reflectance from visible to NIR Snow → High reflectance in visible , low in SWIR ✔ Why Spectral Signature Matters It allows: Land cover classification Chan...

Model GIS object attribute entity

These concepts explain different ways of organizing, storing, and representing geographic information in a Geographic Information System (GIS) . They include database design models (ER model), data structure models (Object and Attribute models), and spatio-temporal representations that integrate location, entities, and time . Together, they help GIS manage both spatial data (where things are) and descriptive information (what they are and how they change over time) . 1. Object-Based Model (Object-Oriented Data Model) The Object-Based Model treats geographic features as independent objects that combine spatial geometry and descriptive attributes within a single structure. Core Concept: Each geographic feature (such as a building, road, or river ) is represented as a self-contained object that stores both: Geometry – location and shape (point, line, polygon) Attributes – descriptive properties (name, type, length, capacity) Unlike older georelational models , which stored spatial ...

GIS data continuous discrete ordinal interval ratio

In Geographic Information Systems (GIS) , data is categorized based on its nature (discrete or continuous) and its measurement scale (nominal, ordinal, interval, or ratio). These distinctions influence how the data is collected, analyzed, and visualized. Let's break down these categories with concepts, terminologies, and examples: 1. Discrete Data Discrete data is obtained by counting distinct items or entities. Values are finite and cannot be infinitely subdivided. Characteristics : Represent distinct objects or occurrences. Commonly represented as vector data (points, lines, polygons). Values within a range are whole numbers or categories. Examples : Number of People : Counting individuals on a train or in a hospital. Building Types : Categorizing buildings as residential, commercial, or industrial. Tree Count : Number of trees in a specific area. 2. Continuous Data Continuous data is obtained by measuring phenomena that can take any value within a range...

Vineesh V, Geography

Search This Blog