Rising Temperatures in Kisumu, Kenya
A Raster GIS Approach​
Urban Heat
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Heat waves rank as one of the deadliest natural hazards, and they claim more lives than all other extreme weather and natural disaster events combined. Unlike other natural hazards that often show immediate signs of destruction, heat waves may not be immediately noticeable in terms of damage. Yet, they pose a significant threat to life and have the potential to severely disrupt vital infrastructure.
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Before exploring the city of Kisumu, it's crucial to grasp the concept of the Urban Heat Island (UHI) effect. This phenomenon is characterized by urban regions having higher temperatures compared to their adjacent rural areas. The main cause of this temperature difference is human activities. Factors such as the heat-absorbing materials used in construction, heat emissions from vehicles and buildings, and the lack of vegetation cover significantly contribute to this effect.
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Context
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Kenya is on the brink of a pivotal transformation, aiming to achieve the ambitious goals outlined in Vision 2030. Kenya faces several key challenges in this journey, such as managing the pressures of rapid urbanization on its infrastructure, ensuring access to healthcare which is crucial for societal progress, and safeguarding human rights which are essential to the dignity of its people. Tackling these issues is essential for guaranteeing that the fruits of economic growth are shared fairly, ensuring that development is both sustainable and inclusive.
Kisumu is a port city in western Kenya at 1,131 m (3,711 ft) elevation. The port was founded in 1901 as the main inland terminal of the Uganda Railway and named Port Florence. As Kenya's third-largest city, Kisumu is a microcosm of the country's development trajectory. It grapples with the demands of urbanization while striving to provide for its residents' health, well-being, and rights. For a detailed exploration of Kisumu and its surroundings, a map is available below to provide a comprehensive view of the area​.
Kisumu's urban footprint today showcases a complex interplay of growth, history, and diverse land uses. The city, evolving from its historical origins, now balances modern development with its cultural and historical heritage. Its expansion reflects a range of functionalities, from residential and commercial spaces to industrial areas, all interwoven into the city's unique character. Colonial segregation in the past has given rise to a belt of informal settlements on the city's periphery, emphasizing the developmental challenges the city confronts. Today, approximately half of Kisumu's residents live in these informal areas.
The image below highlights the distribution of open spaces in Kisumu, revealing a stark unevenness in their spatial allocation. Green spaces, which are crucial for mitigating the urban heat island effect and enhancing the quality of life, appear to be concentrated in certain areas while notably absent in others.
Kisumu is grappling with the escalating challenge of urban heat, a phenomenon that particularly affects its most vulnerable citizens – women, children, and the elderly – in the vast informal settlements that house over half of its population.
The rising temperatures in Kisumu's first rainfall season and the increased frequency of extremely hot days, particularly in the second season, are likely to exacerbate the urban heat island effect, leading to heightened health risks and strain on water and energy resources. Over the long term, these climatic shifts could undermine agricultural productivity, food security, and economic stability in the region.
The lakeside city, with its hot and humid climate, is a hotspot for malaria, affecting 14 million Kenyans, with a malaria infection rate as high as 27% in 2015 In Kisumu . The city's average daytime temperature of 29.7°C, escalating to over 37°C during heatwaves, significantly increases heat-related health risks and issues like dehydration, cardiac problems, and respiratory conditions, affecting the most vulnerable populations.
The significant shortfall in Kisumu’s green spaces, at a critical low of 0.3 square meters per person (2009), reveals a pressing environmental and public health issue. Far from the World Health Organization's recommendation, this scarcity of urban greenery contributes to the intensification of the urban heat island effect, which can lead to increased temperatures within the city.
Addressing the deficit of green spaces in Kisumu is essential for mitigating these risks. By integrating more green infrastructure like parks, green roofs, and tree-lined streets into urban landscapes, cities can improve air quality, reduce heat, and provide much-needed recreational areas for their citizens, fostering a healthier, more sustainable urban environment.
Land Surface Temperature
Land Surface Temperature (LST) is defined by NASA's Earth Observatory as the temperature of the Earth's surface, felt when touched at a specific location. It is increasingly important in various research fields, including climate change, hydrology, agriculture, and urban land use. The development of remote sensing technology has simplified the measurement of LST over time and space by capturing its thermal radiance. LST plays a crucial role in governing various environmental, biological, chemical, and socio-economic processes on Earth.
Normalized Difference Vegetation Index (NDVI), Brightness Temperature (BT), and Land Surface Emissivity (LSE) are factors that will be considered in the calculation process as well as making use of Landsat 7 and Landsat 8 thermal bands, explained in the next section.
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Using Remote Sensing and GIS Analysis to Determine Urban Heat
This analysis delves into the process of measuring urban heat using advanced remote sensing and Geographic Information System (GIS) methods via ArcGIS Pro. It provides a comprehensive guide for analyzing the urban heat island effect in specific areas, contributing to global efforts to address this environmental issue.
The analysis incorporates several critical indicators:
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The Normalized Difference Vegetation Index (NDVI) is crucial for evaluating vegetation health and density, playing a significant role in understanding urban heat dynamics.
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The Proportional Vegetation Index (PVI) helps in assessing vegetation coverage, shedding light on the cooling effects of urban greenery.
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Brightness Temperature is key in identifying urban areas contributing to heat island effects.
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Error Correction is vital for the precision of temperature and vegetation data.
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Top of Atmosphere (TOA) Reflectance measures surface reflectance, crucial for accurate land surface temperatures.
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Lastly, Land Surface Temperature (LST) is essential for illustrating the intensity of urban heat islands.
The integration of these factors into GIS analysis provides a robust framework to quantify, comprehend, and mitigate the rising temperatures in urban landscapes, aiding in the development of cooler and more sustainable urban habitats.
The ultimate goal is to foster urban environments that are not only more temperate but also more liveable, aligning with global sustainability goals.
NDVI Loss Over Past Five Years
As discussed in the previous section, the Normalized Difference Vegetation Index (NDVI) is an essential remote sensing tool for evaluating vegetation health and density. It operates by analyzing the differential reflectance properties of near-infrared and red light. Vegetation typically reflects more near-infrared light and absorbs red light, allowing NDVI to effectively gauge vegetation presence and condition.
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The NDVI value ranges from -1 to +1, where higher values indicate greater density and health of vegetation. Since healthy vegetation will reflect more near-infrared and absorb more red light, it results in higher NDVI values. By monitoring NDVI over time, changes in vegetation health due to varying climatic conditions can be observed and analyzed, which is particularly important for managing agricultural activities, assessing drought conditions, and studying ecological responses to climate change.
The image above depicts the NDVI loss in Kisumu over a five-year period, highlighted by the extensive red areas. These areas represent a significant reduction in vegetation density and health, indicating environmental changes that could impact the region's climate and ecology. The majority of vegetation loss in Kisumu is concentrated in the northern hilly regions and the southern wetlands, along with a noticeable decrease in the peri-urban agricultural zones.
Land Surface Temperature Change from 2001-2022
Using the calculations for Land Surface Temperature and after standardizing data for the years 2001 and 2022, the resulting map illustrates a significant rise in Kisumu's temperatures over the twenty-year span. Over the years, Kisumu's temperatures have been on the rise, a trend that is particularly concerning as cities in the global south are more vulnerable to the impacts of climate change.
Site Introduction
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Zooming into Kisumu reveals a key area along the Kisumu bypass road, a hub linking formal and informal zones. This strategic location is part of the major freight routes to Nairobi and serves as a vital component of the transit corridor, presenting significant opportunities for urban transformation. Spanning 3 kilometers along the bypass, it juxtaposes one of Kisumu's largest informal settlements, Manyatta, with the structured layout of the formal city.
Generation of Urban Heat Line and Stack Profile
Delving deeper into the focused section along Kisumu's bypass highway, I used a stack profile analysis to measure the urban heat and average temperatures along this transect. This method provided insights into the temperature changes between 2001 and 2022, revealing the extent of climatic shifts in the area over the two decades.
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The Stack Profile is a graphing tool for depicting line feature variations over a surface dataset, such as rasters or terrains. For visualizing urban heat, a line shapefile, termed 'urban heat line,' is drawn over Land Surface Temperature (LST) data at a targeted location as shown in the figure. The Stack Profile leverages this line to graph LST variations, plotting the temperatures recorded along it, indicated by "First_z" values, to reflect the urban thermal environment.
The spatiotemporal analysis of urban heat using Land Surface Temperature (LST) data for the years 2001 and 2022 provides crucial insights into the thermal dynamics of urban environments in the city, particularly along the specific site. A mean temperature increase of 4 degrees Celsius in two decades is substantial and signals a critical need for strategies to manage and mitigate urban cooling trends effectively.
The Way Forward
In response to the escalating urban temperatures and health risks, particularly in the context of the Global South and cities like Kisumu, a comprehensive approach is essential for building urban resilience.
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Urban Design Innovation: Incorporate greenery and reflective materials in city planning to combat the heat island effect in Kisumu.
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Public Awareness Efforts: Launch educational campaigns in Kisumu that use local dialects and cultural narratives to teach about the dangers of heatwaves and survival tactics.
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Healthcare Upgrades: Enhance Kisumu's medical facilities with the necessary tools and training to handle a surge in heat-related conditions, ensuring widespread access and preventive education.
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Ongoing Climate Research: Support continuous research in Kisumu to track temperature shifts and their health consequences, guiding urban and health policy decisions.
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Establishment of Cooling Havens: Create accessible cooling sites in Kisumu's densely populated and at-risk areas to provide relief from intense heat, particularly for those lacking home cooling systems.
