scholarly journals Interactions between deforestation, landscape rejuvenation, and shallow landslides in the North Tanganyika – Kivu Rift region, Africa

2020 ◽  
Author(s):  
Arthur Depicker ◽  
Gerard Govers ◽  
Liesbet Jacobs ◽  
Benjamin Campforts ◽  
Judith Uwihirwe ◽  
...  
Keyword(s):  
Slope Failure ◽  
Land Use Changes ◽  
Extreme Rainfall ◽  
Google Earth ◽  
Shallow Landslides ◽  
Extreme Rainfall Events ◽  
Landslide Activity ◽  
Erosion Rates ◽  
The North ◽  
The Impact

Abstract. Deforestation increases landslide activity over short, contemporary timescales. However, over longer timescales the location and timing of landsliding is controlled by the interaction between uplift and fluvial incision. Yet, the interaction between (human-induced) deforestation and landscape evolution has hitherto not been explicitly considered. We address this issue in the North Tanganyika-Kivu Rift region (East African Rift). In recent decades, the regional population has grown exponentially and the associated expansion of cultivated and urban land has resulted in widespread deforestation. On a much longer time scale, tectonic uplift has forged two parallel mountainous Rift shoulders that are continuously rejuvenated through knickpoint retreat, enforcing topographic steepening. In order to link deforestation and rejuvenation to landslide erosion, we compiled an inventory of nearly 8,000 recent shallow landslides in Google Earth© imagery from 2000–2019. To accurately calculate landslide erosion rates, we developed a new methodology to remediate inventory biases linked to the spatial and temporal inconsistency of this satellite imagery. We find that erosion rates in rejuvenated landscapes are roughly 40 % higher than in the surrounding relict landscapes, upstream of retreating knickpoints and outside of the Rift shoulders. This difference is due to the generally steeper relief in rejuvenated landscapes which more than compensates for the fact that rejuvenated slopes, when compared to similarly angled slopes in relict zones, often display a somewhat lower landslide erosion rate. These lower rates in the rejuvenated landscapes could be the result of a drier climate, the omission of earthquake-induced landslide events in our landslide inventory, and potentially a smaller regolith stock. More frequent extreme rainfall events in the relict zones, and possibly the presence of a thicker regolith, cause a stronger landslide response to deforestation compared to rejuvenated landscapes. Overall, deforestation initiates a landslide peak that lasts approximately 15 years and increases landslide erosion by a factor 2 to 8. Eventually, landslide erosion in deforested land falls back to a level similar to that observed under forest conditions, most likely due to the depletion of the most unstable regolith. Landslides are not only more abundant in rejuvenated landscapes but are also smaller in size, which may be a consequence of the seismic activity that fractures the bedrock and reduces the minimal critical area for slope failure. With this paper, we highlight the importance of considering the geomorphological context when studying the impact of recent land use changes on landslide activity.

scholarly journals Interactions between deforestation, landscape rejuvenation, and shallow landslides in the North Tanganyika–Kivu rift region, Africa

2021 ◽  
Vol 9 (3) ◽  
pp. 445-462
Author(s):  
Arthur Depicker ◽  
Gerard Govers ◽  
Liesbet Jacobs ◽  
Benjamin Campforts ◽  
Judith Uwihirwe ◽  
...  
Keyword(s):  
Slope Failure ◽  
Land Use Changes ◽  
Google Earth ◽  
Shallow Landslides ◽  
Extreme Rainfall Events ◽  
Landslide Occurrence ◽  
Landslide Activity ◽  
Erosion Rates ◽  
The North ◽  
The Impact

Abstract. Deforestation is associated with a decrease in slope stability through the alteration of hydrological and geotechnical conditions. As such, deforestation increases landslide activity over short, decadal timescales. However, over longer timescales (0.1–10 Myr) the location and timing of landsliding is controlled by the interaction between uplift and fluvial incision. Yet, the interaction between (human-induced) deforestation and landscape evolution has hitherto not been explicitly considered. We address this issue in the North Tanganyika–Kivu rift region (East African Rift). In recent decades, the regional population has grown exponentially, and the associated expansion of cultivated and urban land has resulted in widespread deforestation. In the past 11 Myr, active continental rifting and tectonic processes have forged two parallel mountainous rift shoulders that are continuously rejuvenated (i.e., actively incised) through knickpoint retreat, enforcing topographic steepening. In order to link deforestation and rejuvenation to landslide erosion, we compiled an inventory of nearly 8000 recent shallow landslides in © Google Earth imagery from 2000–2019. To accurately calculate landslide erosion rates, we developed a new methodology to remediate inventory biases linked to the spatial and temporal inconsistency of this satellite imagery. Moreover, to account for the impact of rock strength on both landslide occurrence and knickpoint retreat, we limit our analysis to rock types with threshold angles of 24–28∘. Rejuvenated landscapes were defined as the areas draining towards Lake Kivu or Lake Tanganyika and downstream of retreating knickpoints. We find that shallow landslide erosion rates in these rejuvenated landscapes are roughly 40 % higher than in the surrounding relict landscapes. In contrast, we find that slope exerts a stronger control on landslide erosion in relict landscapes. These two results are reconciled by the observation that landslide erosion generally increases with slope gradient and that the relief is on average steeper in rejuvenated landscapes. The weaker effect of slope steepness on landslide erosion rates in the rejuvenated landscapes could be the result of three factors: the absence of earthquake-induced landslide events in our landslide inventory, a thinner regolith mantle, and a drier climate. More frequent extreme rainfall events in the relict landscapes, and the presence of a thicker regolith, may explain a stronger landslide response to deforestation compared to rejuvenated landscapes. Overall, deforestation initiates a landslide peak that lasts approximately 15 years and increases landslide erosion by a factor 2 to 8. Eventually, landslide erosion in deforested land falls back to a level similar to that observed under forest conditions, most likely due to the depletion of the most unstable regolith. Landslides are not only more abundant in rejuvenated landscapes but are also smaller in size, which may again be a consequence of a thinner regolith mantle and/or seismic activity that fractures the bedrock and reduces the minimal critical area for slope failure. With this paper, we highlight the importance of considering the geomorphological context when studying the impact of recent land use changes on landslide activity.

scholarly journals Operational tools to help stakeholders to protect and alert municipalities facing uncertainties and changes in karst flash floods

2015 ◽  
Vol 370 ◽  
pp. 201-208 ◽  
Author(s):  
V. Borrell Estupina ◽  
F. Raynaud ◽  
N. Bourgeois ◽  
L. Kong-A-Siou ◽  
L. Collet ◽  
...  
Keyword(s):  
Land Use ◽  
Real Time ◽  
Land Use Changes ◽  
Extreme Rainfall ◽  
Flash Floods ◽  
Uncertain Information ◽  
Extreme Rainfall Events ◽  
Flood Peak ◽  
Planning Decisions ◽  
Graphical Tool

Abstract. Flash floods are often responsible for many deaths and involve many material damages. Regarding Mediterranean karst aquifers, the complexity of connections, between surface and groundwater, as well as weather non-stationarity patterns, increase difficulties in understanding the basins behaviour and thus warning and protecting people. Furthermore, given the recent changes in land use and extreme rainfall events, knowledge of the past floods is no longer sufficient to manage flood risks. Therefore the worst realistic flood that could occur should be considered. Physical and processes-based hydrological models are considered among the best ways to forecast floods under diverse conditions. However, they rarely match with the stakeholders' needs. In fact, the forecasting services, the municipalities, and the civil security have difficulties in running and interpreting data-consuming models in real-time, above all if data are uncertain or non-existent. To face these social and technical difficulties and help stakeholders, this study develops two operational tools derived from these models. These tools aim at planning real-time decisions given little, changing, and uncertain information available, which are: (i) a hydrological graphical tool (abacus) to estimate flood peak discharge from the karst past state and the forecasted but uncertain intense rainfall; (ii) a GIS-based method (MARE) to estimate the potential flooded pathways and areas, accounting for runoff and karst contributions and considering land use changes. Then, outputs of these tools are confronted to past and recent floods and municipalities observations, and the impacts of uncertainties and changes on planning decisions are discussed. The use of these tools on the recent 2014 events demonstrated their reliability and interest for stakeholders. This study was realized on French Mediterranean basins, in close collaboration with the Flood Forecasting Services (SPC Med-Ouest, SCHAPI, municipalities).

Reconstruction of a realistic rainfall field for extreme events happened in mountain area

2021 ◽  
Author(s):  
Andrea Abbate ◽  
Laura Longoni ◽  
Monica Papini
Keyword(s):  
Extreme Events ◽  
Temporal Distribution ◽  
Extreme Rainfall ◽  
Shallow Landslides ◽  
Mountain Areas ◽  
Mountain Area ◽  
Extreme Rainfall Events ◽  
Lombardy Region ◽  
Rain Gauges ◽  
Rainfall Model

<p>In the field of hydrogeological risk, rainfalls represent the most important triggering factor for superficial terrain failures such as shallow landslides, soil slips and debris flow. The availability of local rain gauges measurements is fundamental for defining the cause-effect relationship for predicting failure scenarios. Unfortunately, these hydrogeological phenomena are typical triggered over mountains regions where the density of the ground-based meteorological network is poor, and the local effects caused by mountains topography can change dramatically the spatial and temporal distribution of rainfall. Therefore, trying to reconstruct a representative rainfall field across mountain areas is a challenge but is a mandatory task for the interpretation of triggering causes. We present a reanalysis of an ensemble of extreme rainfall events happened across central Alps and Pre-Alps, in the northern part of Lombardy Region, Italy. We have investigated around some critical aspects such as their intensity and persistency also proposing a modelling of their meteorological evolution, using the Linear Upslope-Rainfall Model (LUM). We have considered this model because it is designed for describing the mechanism of orographic precipitation intensification that was identified as the main cause of that extreme events. To test and calibrate the LUM model we have considered local rain gauges data because they represent the effective rainfall poured on the ground. These punctual data are generally considered for landslide assessment, in particular for rainfall induced phenomena such as shallow landslides and debris flows. Considering our test cases, the results obtained have shown that the LUM has been able to reproduce accurately the rainfall field. In this regard, LUM model can help to address further information around those ungauged area where rainfall estimation could be critical for evaluating the hazard. We are conscious that our and other studies around this topic would be propaedeutic in the next future for the adoption of an integrated framework among the real-time meteorological modelling and the hydrogeological induced risk assessment and prevision.</p>

Does extreme rainfall lead to heavy losses in the food industry?

2019 ◽  
Vol 32 (2) ◽  
pp. 244-266
Author(s):  
Edimilson Costa Lucas ◽  
Wesley Mendes-Da-Silva ◽  
Gustavo Silva Araujo
Keyword(s):  
Stock Returns ◽  
Food Production ◽  
Food Industry ◽  
Extreme Rainfall ◽  
Extreme Weather ◽  
Extreme Weather Events ◽  
Extreme Rainfall Events ◽  
Content Type ◽  
Weather Events ◽  
The Impact

Purpose Managing the risks associated to world food production is an important challenge for governments. A range of factors, among them extreme weather events, has threatened food production in recent years. The purpose of this paper is to analyse the impact of extreme rainfall events on the food industry in Brazil, a prominent player in this industry. Design/methodology/approach The authors use the AR-GARCH-GPD hybrid methodology to identify whether extreme rainfall affects the stock price of food companies. To do so, the authors collected the daily closing price of the 16 food industry companies listed on the Brazilian stock exchange (B3), in January 2015. Findings The results indicate that these events have a significant impact on stock returns: on more than half of the days immediately following the heavy rain that fell between 28 February 2005 and 30 December 2014, returns were significantly low, leading to average daily losses of 1.97 per cent. These results point to the relevance of the need for instruments to hedge against weather risk, particularly in the food industry. Originality/value Given that extreme weather events have been occurring more and more frequently, financial literature has documented attempts at assessing the economic impacts of weather changes. There is little research, however, into assessing the impacts of these events at corporate level.

scholarly journals Rainfall Threshold for Shallow Landslides Initiation and Analysis of Long-Term Rainfall Trends in a Mediterranean Area

Atmosphere ◽  
2020 ◽  
Vol 11 (12) ◽  
pp. 1367
Author(s):  
Anna Roccati ◽  
Guido Paliaga ◽  
Fabio Luino ◽  
Francesco Faccini ◽  
Laura Turconi
Keyword(s):  
Kendall Test ◽  
Shallow Landslides ◽  
Landslide Risk ◽  
Rainfall Time Series ◽  
Ligurian Sea ◽  
Extreme Rainfall Events ◽  
Mediterranean Countries ◽  
Rainfall Trends ◽  
The Impact

The effects of climate change on landslide activity may have important environmental, socio-economic, and political consequences. In the last decades, several short-term extreme rainfall events affected Mediterranean regions, resulted in damaging geo-hydrological processes and casualties. It is unequivocal that the impact of landslides in several Mediterranean countries is increasing with time, but until now, there has been little or no quantitative data to support these increases. In this paper, both rainfall conditions for the occurrence of shallow landslides and rainfall trends were investigated in the Portofino promontory, which extends in the Ligurian Sea, where heavy rainfall and related ground effects often occur. Adopting a frequentist approach, the empirical intensity-duration threshold was estimated. Our findings highlight that the rainfall intensity required to trigger landslides is lower for the same duration than those expected in other similar environments, suggesting a high susceptibility to rainfall-induced landslides in the Portofino territory. Further, the Mann-Kendall test and Hurst exponent were used for detecting potential trends. Analysis of long-term rainfall time series showed statistically significant increasing trends in short duration precipitation occurrence and rainfall rates, suggesting a possible future scenario with a more frequent exceedance of the threshold triggering value and an increase of landslide risk.

Recent Trends of Desertification in the Maowusu Desert, China

1983 ◽  
Vol 10 (3) ◽  
pp. 213-224 ◽  
Author(s):  
Shiu-Hung Luk
Keyword(s):  
Land Use ◽  
Raw Materials ◽  
Land Use Changes ◽  
Shaanxi Province ◽  
Contributory Factor ◽  
Major Step ◽  
North West ◽  
The North ◽  
Land Use Policies ◽  
The Impact

In the Maowusu Desert—which in the south-east encompasses part of the Yulin Region, Shaanxi Province, and in the north-west the Ih Ju League, Inner Mongolia Autonomous Region—desertification trends in relation to the impact of droughts and land-use changes were investigated. Data derived from Earth resources technology satellites (LANDSAT I and LANDSAT II, 1974–1978), and Chinese documentary sources, were used for the analysis. It was found that desert ‘expansion’ occurred during 1953–76, but the rates of expansion varied over time and space, relatively rapid desertification being observed for 1959–63 and 1971–76. The bulk of the expansion was located in the more arid Ih Ju League. The mean annual rate of areal expansion was 6.4% during 1958–71. By comparing the desertification rates with precipitation and land-use information, it was established that droughts have only accentuated the desertification process. The primary cause of desert expansion is the excessive clearing of land for rain-fed agriculture as well, of course, as overgrazing. Another contributory factor was culling of vegetation for fuel and raw materials for handicraft industries.Efforts have been expended on desert control since the mid-1950s, resulting in the arresting of desertification in some local areas. The individual success stories demonstrate that, with mass participation, effective desert control can be achieved by using low-level technology. However, the Chinese programme of desert control was not conceived as a comprehensive programme. Control activities relied almost exclusively on vegetational methods, and they were seldom coordinated with land-use policies as well as with the planning of energy supplies. The negligence of the fundamental conflict between expanding agricultural activities and desert control has led to a net desert expansion in the last 30 years. Recognition of this fundamental conflict and implementation of mitigative land-use policies, would be a major step towards resolving the desertification problem in the Maowusu Desert.

scholarly journals Evaluation of Rainfall-Triggered Debris Flows under the Impact of Extreme Events: A Chenyulan Watershed Case Study, Taiwan

Water ◽  
2021 ◽  
Vol 13 (16) ◽  
pp. 2201
Author(s):  
Jinn-Chyi Chen ◽  
Wen-Shun Huang
Keyword(s):  
Debris Flow ◽  
Extreme Events ◽  
Debris Flows ◽  
Extreme Rainfall ◽  
Extreme Rainfall Event ◽  
Extreme Rainfall Events ◽  
Hourly Rainfall ◽  
Central Taiwan ◽  
The Impact

This study examined the conditions that lead to debris flows, and their association with the rainfall return period (T) and the probability of debris flow occurrence (P) in the Chenyulan watershed, central Taiwan. Several extreme events have occurred in the Chenyulan watershed in the past, including the Chi-Chi earthquake and extreme rainfall events. The T for three rainfall indexes (i.e., the maximum hourly rainfall depth (Im), the maximum 24-h rainfall amount (Rd), and RI (RI = Im× Rd)) were analyzed, and the T associated with the triggering of debris flows is presented. The P–T relationship can be determined using three indexes, Im, Rd, and RI; how it is affected and unaffected by extreme events was developed. Models for evaluating P using the three rainfall indexes were proposed and used to evaluate P between 2009 and 2020 (i.e., after the extreme rainfall event of Typhoon Morakot in 2009). The results of this study showed that the P‒T relationship, using the RI or Rd index, was reasonable for predicting the probability of debris flow occurrence.

Fire and rain are one: extreme rainfall events predict wildfire extent in an arid grassland

2020 ◽  
Vol 29 (8) ◽  
pp. 702 ◽  
Author(s):  
Elise M. Verhoeven ◽  
Brad R. Murray ◽  
Chris R. Dickman ◽  
Glenda M. Wardle ◽  
Aaron C. Greenville
Keyword(s):  
Landsat Imagery ◽  
Extreme Rainfall ◽  
Environmental Drivers ◽  
Annual Rainfall ◽  
Extreme Rainfall Events ◽  
Study Region ◽  
Rainfall Events ◽  
The North ◽  
The Mean ◽  
Wildfire Regimes

Assessing wildfire regimes and their environmental drivers is critical for effective land management and conservation. We used Landsat imagery to describe the wildfire regime of the north-eastern Simpson Desert (Australia) between 1972 and 2014, and to quantify the relationship between wildfire extent and rainfall. Wildfires occurred in 15 of the 42 years, but only 27% of the study region experienced multiple wildfires. A wildfire in 1975 burned 43% of the region and is the largest on record for the area. More recently, a large wildfire in 2011 reburned areas that had not burned since 1975 (47% of the 2011 wildfire), as well as new areas that had no record of wildfires (25% of the 2011 wildfire). The mean minimum wildfire return interval was 27 years, comparable with other spinifex-dominated grasslands, and the mean time since last wildfire was 21 years. Spinifex-dominated vegetation burned most frequently and over the largest area. Extreme annual rainfall events (> 93rd percentile) effectively predicted large wildfires occurring 2 years after those events. Extreme rainfall is predicted to increase in magnitude and frequency across central Australia, which could alter wildfire regimes and have unpredictable and far-reaching effects on ecosystems in the region’s arid landscapes.

Inventory and preliminary assessment of natural hazards in Kigezi highlands, South Western Uganda

2021 ◽  
Author(s):  
Violet Kanyiginya ◽  
Ronald Twongyirwe ◽  
Grace Kagoro ◽  
David Mubiru ◽  
Matthieu Kervyn ◽  
...  
Keyword(s):  
Land Use ◽  
Natural Hazards ◽  
Natural Hazard ◽  
Rainfall Variability ◽  
Land Use Changes ◽  
Satellite Image ◽  
Google Earth ◽  
Landscape Characteristics ◽  
Western Uganda ◽  
The Impact

<p>Uganda is regularly affected by multiple natural hazards, including floods, droughts, earthquakes, landslides and windstorms. This is due to a combination of natural biophysical factors such as steep topography, intense rainfall, variability of dry and rain seasons and high weathering rates. In addition, high population density, deforestation and other human-induced land use changes, and high poverty levels are believed to have an influence on the patterns of natural hazards and their impacts in the region. Despite this, there are limited studies that assess where and when natural hazards occur in Uganda, and a dearth of information on the processes involved. In addition, drivers and earth/landscape characteristics controlling the occurrence of natural hazards in the country remain poorly understood despite the high need for effective disaster risk reduction. Here, we present the ongoing methodological research framework and the first results of a study whose main objective is to understand the spatial and temporal occurrence of natural hazards that affect the Kigezi Highlands of south western Uganda and their interactions. To this end, the study is undertaking a comprehensive regional hazard inventory consisting of satellite image analysis, field surveys and exploration of literature and archives. Historical aerial photos and interviews with the elderly are important tools to analyze the impact of multi-decadal human-induced land use changes on natural hazard occurrences. Meanwhile, a network of 15 geo-observers, i.e. citizens of local communities distributed across representative landscapes of the study area, was established in December 2019. Trained at using smartphone technology, they collect information (processes and impacts) on seven different natural hazards (droughts, earthquakes, floods, hailstorms, landslides, lightning, and windstorms) whenever they occur.  During the first 12 months, 204 natural hazard events with accurate timing information have been reported by the geo-observers. Combined to field survey, these recent events have been associated mainly with the occurrence of > 3000 shallow landslides and 30 floods, frequently in co-occurrence and triggered by heavy rainfall. Additional inventory from Google Earth and Planet imagery covering a region much larger than that of the geo-observer network and a time window of more than 10 years shows an extra 230 landslide and flood occurrences, while archives and literature indicate 226 natural hazard events over the last 30 years. The preliminary results already demonstrate the value of citizen-science in producing highly detailed natural hazard inventory. A combination of different inventory methods improves the level of accuracy in understanding the spatial-temporal distribution of natural hazards.</p>

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