Cyclone Precipitation Research Articles

Impact of winter SST anomaly in tropical Eastern Pacific on following summer tropical cyclone precipitation in China

AbstractThis study reveals a significant effect of the winter sea surface temperature (SST) anomaly (SSTA) in the tropical Eastern Pacific (TEP) on the following summer tropical cyclone precipitation (TCP) in mainland China. During the period 1979–2015, the positive winter TEP SSTA forces a SST zonal tripole pattern anomaly, which is positive SSTA in the tropical Indian Ocean (TIO), negative SSTA in the tropical Western Pacific (TWP), and positive SSTA in the TEP. This SSTA pattern triggers two simultaneous zonal circulation anomalies. One exhibits lower‐level convergent winds, mid‐tropospheric ascendant flows and upper‐level divergent winds over the Western TIO, and reversed situations over the TWP, producing anomalous lower‐level easterlies and upper‐level westerlies between the TIO and TWP. The other shows lower‐level convergence, mid‐tropospheric ascent, upper‐level divergence over the TEP, and reversed situations over the TWP, which create lower‐level westerlies and upper‐level easterlies between the TWP and TEP. The two circulation anomalies further warm the TEP (Western TIO) by driving ambient warm water toward this region and cool the TWP by inducing local upwelling, which facilitates the persistence of the anomalies until the summer. Consequently, the lower‐level negative vorticity, strong vertical wind shear and the lower‐level anticyclone anomalies over most of the Western North Pacific (WNP) are accompanied with anomalous mid‐tropospheric westerlies over the coastal regions in mainland China, suppressing TC genesis and movement towards mainland China so as to decrease the summer TCP in mainland China. These results provide an important implication that the winter TEP SSTA is a potential indicator for seasonal prediction of the WNP TC activity and the TCP in mainland China.

On the frequency changes of cyclones affecting precipitation in the Rood Zard basin, Iran

Changes in cyclones in a region may lead to variations in the precipitation conditions of that region. The current study aimed at examining changes in the frequency of cyclones affecting precipitation in the Rood Zard basin, Iran, during 1976 to 2014. To this end, 1000 hPa maps of NCEP/NCAR and the daily precipitation data of 16 stations located in the basin of the Rood Zard were adopted. The results showed that the frequency of cyclones, their consequent precipitation, and the overall amount of cyclonic precipitation experienced a declining trend over the abovementioned period. The findings of the present study are in line with those of previous ones conducted on other areas in the Northern Hemisphere. Following the examination of mean differences in the cyclone frequency during the understudy period, a significant jump was also observed which tends to delay cyclones’ activities compared with those accruing in the previous years. Further, it was discovered that the seasons of cyclonic precipitation became shorter over recent years. The investigation into these changes can be attributed to climate change discussed in a bulk of previous studies. The existing cycles in the frequency of cyclones and cyclonic precipitation showed the presence of similar (3 and 4.6 years) cycles in both factors. Experts in the field have attributed these short-term cycles to quasi-biennial oscillation (QBO) in the troposphere, ENSO, and similar phenomena taking place frequently in climate change context.

Linking Atmospheric Rivers and Warm Conveyor Belt Airflows

Abstract Extreme precipitation associated with extratropical cyclones can lead to flooding if cyclones track over land. However, the dynamical mechanisms by which moist air is transported into cyclones is poorly understood. In this paper we analyze airflows within a climatology of cyclones in order to understand how cyclones redistribute moisture stored in the atmosphere. This analysis shows that within a cyclone’s warm sector the cyclone-relative airflow is rearwards relative to the cyclone propagation direction. This low-level airflow (termed the feeder airstream) slows down when it reaches the cold front, resulting in moisture flux convergence and the formation of a band of high moisture content. One branch of the feeder airstream turns toward the cyclone center, supplying moisture to the base of the warm conveyor belt where it ascends and precipitation forms. The other branch turns away from the cyclone center exporting moisture from the cyclone. As the cyclone travels, this export results in a filament of high moisture content marking the track of the cyclone (often used to identify atmospheric rivers). We find that both cyclone precipitation and water vapor transport increase when moisture in the feeder airstream increases, thus explaining the link between atmospheric rivers and the precipitation associated with warm conveyor belt ascent. Atmospheric moisture budgets calculated as cyclones pass over fixed domains relative to the cyclone tracks show that continuous evaporation of moisture in the precyclone environment moistens the feeder airstream. Evaporation behind the cold front acts to moisten the atmosphere in the wake of the cyclone passage, potentially preconditioning the environment for subsequent cyclone development.

Development of Electrostatic Cyclone Precipitator for Marine Diesel Engines - PM Reduction with Vertical Type ESP-cyclone System in Exhaust Gas from Two-Stroke Marine Diesel Engine

Development of Electrostatic Cyclone Precipitator for Marine Diesel Engines - PM Reduction with Vertical Type ESP-cyclone System in Exhaust Gas from Two-Stroke Marine Diesel Engine

Precipitation Microphysics of Tropical Cyclones Over the Western North Pacific Based on GPM DPR Observations: A Preliminary Analysis

AbstractUsing observations from the dual‐frequency precipitation radar (DPR) onboard the Global Precipitation Measurement mission (GPM) satellite, this study analyzes the microphysical structures and processes of tropical cyclone (TC) precipitation over the western North Pacific in terms of different precipitation efficiency indices (PEIs). The statistical results show that the mean mass‐weighted mean diameter of raindrops (Dm) at 2 km is 1.67 mm (1.37 mm) for convective (stratiform) precipitating clouds. Precipitating clouds with high PEI have higher liquid water path than nonliquid water path for both convective and stratiform clouds. The mean Dm of convective and stratiform precipitation increases as the PEI increases. The vertical profiles of Dm and reflectivity (Ze) for convective and stratiform precipitating clouds in TCs differ substantially as the PEI changes. Below the melting level, there is a clear decrease (increase) in Dm and Ze toward the surface for clouds with low (high) PEI. In general, clouds within TCs producing the most efficient precipitation are characterized by strong coalescence, not only for small droplets but also for relatively large raindrops; in contrast, the breakup of hydrometeors is the dominant process in convective and stratiform precipitating clouds with low PEI. These results will help validate and improve the hydrometeor parameterization schemes in cloud and climate models.

Physically based storm transposition of four Atlantic tropical cyclones

In this article, a method for the storm transposition of tropical cyclones is presented. This method is physically based as it uses a regional atmospheric model to reconstruct the precipitation depth field from a tropical cyclone, thus crucially conserving the mass, momentum and energy in the system. In this physically based storm transposition method, the tropical cyclone vortex in the simulation initial conditions is first shifted spatially. More precisely, the tropical cyclone at the simulation start date is first separated from its background environment, then shifted, and finally recombined with the background environment. Afterwards, the regional atmospheric model is run as usual to simulate the shifted tropical cyclone and its precipitation depth field. The storm transposition method was then applied to four hurricanes which spawned torrential precipitation in the United States: Hurricanes Floyd (1999), Frances (2004), Ivan (2004), and Isaac (2012), in order to maximize the 72-h precipitation depth over the drainage basin of the city of Asheville, NC. It was observed that the precipitation depth fields changed in both structure and intensity after the physically based storm transposition. Besides, the tropical cyclone tracks were generally very sensitive to changes in the initial conditions, which is expected for a storm system whose dynamics is strongly nonlinear. In particular, it was found that a small change in the location of the initial tropical cyclone vortex may result in a very different track, allowing the tropical cyclone's precipitation depth field to move over the target area.

Impacts of Climate Change on Tropical Cyclones in the Western North Pacific Basin. Part II: Late Twenty-First Century Projections

ABSTRACT This paper reviews the latest studies on the relationship between projected late 21st century climate changes and tropical cyclone (TC) activity in the western North Pacific (WNP) basin, which is the region of the United Nations Economic and Social Commission for Asia and the Pacific (ESCAP)/World Meteorological Organization (WMO) Typhoon Committee members. Existing studies of projected changes of TC activity in this basin, such as frequency, intensity, precipitation, genesis location and track pattern are summarized, based on an assumed A1B future climate change scenario. A review of available studies on projected future changes in WNP landfalling TC activity is also included. While it remains uncertain whether there has been any detectable human influence on tropical cyclone frequency, intensity, precipitation, track, or related aggregated storm activity metrics in the basin, modeling studies suggest changes in future tropical cyclone activity for the WNP basin. More models project decreases than increases in tropical storm frequency (range − 70% to + 60%); most studies project an increase in the TC intensity (range − 3% to + 18%); and all six available studies that include the WNP basin project increases in TC precipitation rates (range + 5 to + 30%).

Impacts of Climate Change on Tropical Cyclones in the Western North Pacific Basin. Part I: Past Observations

ABSTRACT This paper reviews the current state of the science on the relationship between climate change and historical tropical cyclone (TC) activity in the western North Pacific (WNP) basin, which is the region of the ESCAP/ WMO Typhoon Committee members. Existing studies of observed changes of TC activity in this basin, such as frequency, intensity, precipitation, genesis location and track pattern are summarized. Results from a survey on impacts of past TC activity on various members of Typhoon Committee are reported, along with a review of studies of past WNP landfalling TCs. With considerable interannual and interdecadal variations in the TC activity in this basin, it remains uncertain whether there has been any detectable human influence on tropical cyclone frequency, intensity, precipitation, track, or related aggregated storm activity metrics. Also, the issues of homogeneity and consistency of best track data sets in the WNP further add uncertainty to relevant research studies. Observations indicate some regional shifts in TC activity in the basin, such as a decreasing trend in TC occurrence in part of the South China Sea and an increasing trend along the east coast of China during the past 40 years. This change is apparently related to local circulation changes in the eastern Asia and WNP, though the cause of the circulation changes remains unknown.

Future Projection of Tropical Cyclone Precipitation over Japan with a High-Resolution Regional Climate Model

Future Projection of Tropical Cyclone Precipitation over Japan with a High-Resolution Regional Climate Model

Coupling of Precipitation and Cloud Structures in Oceanic Extratropical Cyclones to Large-Scale Moisture Flux Convergence

AbstractPrecipitation (from TMPA) and cloud structures (from MODIS) in extratropical cyclones (ETCs) are modulated by phases of large-scale moisture flux convergence (from MERRA-2) in the sectors of ETCs, which are studied in a new coordinate system with directions of both surface warm fronts (WFs) and surface cold fronts (CFs) fixed. The phase of moisture flux convergence is described by moisture dynamical convergence Qcnvg and moisture advection Qadvt. Precipitation and occurrence frequencies of deep convective clouds are sensitive to changes in Qcnvg, while moisture tendency is sensitive to changes in Qadvt. Increasing Qcnvg and Qadvt during the advance of the WF is associated with increasing occurrences of both deep convective and high-level stratiform clouds. A rapid decrease in Qadvt with a relatively steady Qcnvg during the advance of the CF is associated with high-level cloud distribution weighting toward deep convective clouds. Behind the CF (cold sector or area with polar air intrusion), the moisture flux is divergent with abundant low- and midlevel clouds. From deepening to decaying stages, the pre-WF and WF sectors experience high-level clouds shifting to more convective and less stratiform because of decreasing Qadvt with relatively steady Qcnvg, and the CF experiences shifting from high-level to midlevel clouds. Sectors of moisture flux divergence are less influenced by cyclone evolution. Surface evaporation is the largest in the cold sector and the CF during the deepening stage. Deepening cyclones are more efficient in poleward transport of water vapor.

Comparisons of Gauge, TMPA and IMERG Products for Monsoon and Tropical Cyclone Precipitation in Southern China

The Tropical Rainfall Measuring Mission (TRMM) Multi-satellite Precipitation Analysis (TMPA) and Integrated Multi-satellite Retrievals for Global Precipitation Measurement (GPM) Mission (IMERG) products are compared against 447 quality-controlled rain gauges in southern China (SC) during summer (May to August) for the period 2014–2016. The differences of TMPA and IMERG in measuring the monsoon and tropical cyclone (TC) precipitation, considering the mean spatial patterns, and rainfall intensities are evaluated quantitatively. Statistical analysis shows that IMERG has much higher correlations of precipitation frequency (PF) with gauge observations for monsoon and TC precipitation. However, both satellite-based products show much poorer capability in estimating conditional rainfall and PF for TC precipitation, especially for estimating large conditional rainfall in TC systems. The capability of capturing the precipitation events at different rainfall intensities decreases with the increase of rainfall threshold for both monsoon and TC precipitation. Generally, IMERG exhibits a superior ability to detect precipitation at different rainfall intensities than TMPA. In depicting the diurnal cycles, IMERG shows a much better performance in estimating rainfall and PF for monsoon precipitation than TMPA by revealing the comparable diurnal amplitudes to the rain gauges, whereas TMPA fails to accurately estimate the early morning rainfall and PF. As a successor to TMPA, IMERG is a reliable source of precipitation estimates for future studies on precipitation meteorology.

Theoretical study on submicron particle escape reduced by magnetic confinement effect in low inlet speed electrostatic cyclone precipitators

Based on the idea of suppressing submicron particle escape effectively by applying magnetic field, we propose a novel model design of outer vortex electrostatic cyclone precipitator (ECP) and establish a theoretical model under four-field coupling interaction. The influences of temperature and working voltage on the escape rate of submicron particles with or without magnetic confinement effect are subsequently evaluated. The results indicate that magnetic confinement effect can availably reduce submicron particle escape in ECP. Whether magnetic field exists or not, high working voltage and low temperature are more favorable to confine submicron particles to collection wall surface, however, the increasing effect of low working voltage on the trapping performance is bigger, and the weakening effect of temperature under magnetic confinement effect is smaller than that under non magnetic field. At a certain working voltage or temperature, the enhancing effect of magnetic field on collection efficiency progressively decreases with the increasing magnetic flux density, and the smaller the magnetic flux density is, the stronger the ability of magnetic confinement becomes. The research results provide assistance for designing newly effective ECP and applying magnetic confinement technique to reduce submicron particle escape in industrial applications.

Quantification of Precipitation Asymmetries of Tropical Cyclones Using 16‐Year TRMM Observations

AbstractBoth low and higher wavenumber asymmetries of tropical cyclone (TC) precipitation are quantified from 16 years of Tropical Rainfall Measuring Mission (TRMM) microwave imager rainfall estimates using Fourier decomposition. The energy spectrum of rainfall perturbation and impacts of the storm motion and vertical wind shear to the rainfall asymmetry are analyzed. It is found that the wavenumber 1 perturbation only contributes 37% of the total perturbation energy of total TC precipitation, while over 70% of the total perturbation energy is from the sum of wavenumbers 1 through 6. Most of the total precipitation asymmetry is from the heavy precipitation, and contributions for light and moderate precipitation types are small. The maximum motion‐relative precipitation asymmetry is generally located down motion but shifts cyclonically after adding wavenumber 2–6 components to wavenumber 1. The asymmetry index of wavenumber 1 and 1–6 asymmetries relative to the vertical wind shear is about 2 to 3 times as large as that relative to the storm motion. The vertical wind shear is a more important factor than the storm motion in producing precipitation asymmetry, especially for the wavenumber 1. A dominant downshear left wavenumber‐1 asymmetry maximum is found regardless of the shear vector orientation to the TC motion, the magnitude of the shear value, and the speed of TC motion. However, the maximum asymmetry of wavenumber 1–6 asymmetry becomes downshear right for the subgroup with low shear, fast motion, and the shear vector left to the motion.

A Nowcasting Model for Tropical Cyclone Precipitation Regions Based on the TREC Motion Vector Retrieval with a Semi-Lagrangian Scheme for Doppler Weather Radar

Accurate observational data and reliable prediction models are both essential to improve the quality of precipitation forecasts. The spiraling trajectories of air parcels within a tropical cyclone (TC) coupled with the large sizes of these systems brings special challenges in making accurate short-term forecasts, or nowcasts. Doppler weather radars are ideal instruments to observe TCs when they move over land, and traditional nowcasts incorporate radar data. However, data from dozens of radars must be mosaicked together to observe the entire system. Traditional single-radar-based reflectivity tracking methods commonly employed in nowcasting are not suitable for TCs as they are not able to capture the circular motion of these systems. Thus, this paper focuses on improving short-term predictability of TC precipitation with Doppler weather radar observations based on: a multi-scale motion vector retrieval algorithm, an optimization technique and a semi-Lagrangian advection scheme. Motion fields of precipitation regions are obtained by a multi-level motion vector retrieval algorithm, then corrected and smoothed by the optimization technique using mass and smooth constraints. Predicted precipitation regions are then extrapolated using the semi-Lagrangian advection scheme. A case study of Hurricane Isabel (2003) shows that the combination of these methods may increase reliable rainfall prediction to about 5 h as the TC moves over land.

Observational Constraint for Precipitation in Extratropical Cyclones: Sensitivity to Data Sources

AbstractUsing cyclone-centered compositing and a database of extratropical-cyclone locations, the distribution of precipitation frequency and rate in oceanic extratropical cyclones is analyzed using satellite-derived datasets. The distribution of precipitation rates retrieved using two new datasets, the Global Precipitation Measurement radar–microwave radiometer combined product (GPM-CMB) and the Integrated Multisatellite Retrievals for GPM product (IMERG), is compared with CloudSat, and the differences are discussed. For reference, the composites of AMSR-E, GPCP, and two reanalyses are also examined. Cyclone-centered precipitation rates are found to be the largest with the IMERG and CloudSat datasets and lowest with GPM-CMB. A series of tests is conducted to determine the roles of swath width, swath location, sampling frequency, season, and epoch. In all cases, these effects are less than ~0.14 mm h−1 at 50-km resolution. Larger differences in the composites are related to retrieval biases, such as ground-clutter contamination in GPM-CMB and radar saturation in CloudSat. Overall the IMERG product reports precipitation more often, with larger precipitation rates at the center of the cyclones, in conditions of high precipitable water (PW). The CloudSat product tends to report more precipitation in conditions of dry or moderate PW. The GPM-CMB product tends to systematically report lower precipitation rates than the other two datasets. This intercomparison provides 1) modelers with an observational uncertainty and range (0.21–0.36 mm h−1 near the cyclone centers) when using composites of precipitation for model evaluation and 2) retrieval-algorithm developers with a categorical analysis of the sensitivity of the products to PW.

Impact of aerosols on tropical cyclone-induced precipitation over the mainland of China

In this study, we investigate the impacts of aerosols on tropical cyclone (TC) precipitation that occurred from 1980 to 2014 over China mainland. The TC-induced precipitation is objectively identified based on Western North Pacific (WNP) TC historical track data and daily precipitation data from meteorological stations. Aerosol optical depth (AOD) from the Second Modern-Era Retrospective Analysis for Research and Applications (MERRA-2) is used to represent the amount of aerosol pollution. The long-term variations in AOD and TC precipitation from the past 35 years are analyzed. A significant increasing trend is found for both the relative percentage of TC rainstorm days and the amount of aerosol loading. Together with the decreasing trend in the annual number of TCs affecting China, this indicates that aerosols are invigorating TC precipitation. For the TC precipitation during the study period, the relative occurrence of light rain shows a decreasing trend, while the proportion of heavy rain and rainstorms shows an increasing trend. Meanwhile, the intensity of the TC daily precipitation increases with the elevated pollution level, particularly during the TC initial period and for heavy TC rainfall. These statistical results based on long-term observations suggest that aerosols have a substantial impact on TC precipitation through microphysical effects and have the potential to impact the track, intensity, size, and lifespan of TCs over Southeast Asia.

An examination of extratropical cyclone response to changes in baroclinicity and temperature in an idealized environment

The dynamics and precipitation in extratropical cyclones (ETCs) are known to be sensitive to changes in the cyclone environment, with increases in bulk water vapor and baroclinicity both leading to increases in storm strength and precipitation. Studies that demonstrate this sensitivity have commonly varied either the cyclone moisture or baroclinicity, but seldom both. In a changing climate, in which the near-surface equator to pole temperature gradient may weaken while the bulk water vapor content of the atmosphere increases, it is important to understand the relative response of ETC strength and precipitation to changes in both factors simultaneously. In this study, idealized simulations of ETC development are conducted in a moist environment using a model with a full suite of moist physics parameterizations. The bulk temperature (and water vapor content) and baroclinicity are systematically varied one at a time, then simultaneously, and the effect of these variations on the storm strength and precipitation is assessed. ETC intensity exhibits the well-documented response to changes in baroclinicity, with stronger ETCs forming in higher baroclinicity environments. However, increasing water vapor content produces non-monotonic changes in storm strength, in which storm intensity first increases with increasing environmental water vapor, then decreases above a threshold value. Examination of the storm geographic extent indicates cyclone size also decreases above a threshold value of bulk environmental temperature (and water vapor). Decrease in storm size is concomitant with an increase in the convective fraction of precipitation and a shift in the vertical distribution of latent heating. The results indicate the existence of at least two regimes for ETC development, each of which exhibit significantly different distributions of PV due to differences in timing and location of convective heating.

Evaluation of Extratropical Cyclone Precipitation in the North Atlantic Basin: An analysis of ERA-Interim, WRF, and two CMIP5 models.

The representation of extratropical cyclones (ETCs) precipitation in general circulation models (GCMs) and a weather research and forecasting (WRF) model is analyzed. This work considers the link between ETC precipitation and dynamical strength and tests if parameterized convection affects this link for ETCs in the North Atlantic Basin. Lagrangian cyclone tracks of ETCs in ERA-Interim reanalysis (ERAI), the GISS and GFDL CMIP5 models, and WRF with two horizontal resolutions are utilized in a compositing analysis. The 20-km resolution WRF model generates stronger ETCs based on surface wind speed and cyclone precipitation. The GCMs and ERAI generate similar composite means and distributions for cyclone precipitation rates, but GCMs generate weaker cyclone surface winds than ERAI. The amount of cyclone precipitation generated by the convection scheme differs significantly across the datasets, with GISS generating the most, followed by ERAI and then GFDL. The models and reanalysis generate relatively more parameterized convective precipitation when the total cyclone-averaged precipitation is smaller. This is partially due to the contribution of parameterized convective precipitation occurring more often late in the ETC life cycle. For reanalysis and models, precipitation increases with both cyclone moisture and surface wind speed, and this is true if the contribution from the parameterized convection scheme is larger or not. This work shows that these different models generate similar total ETC precipitation despite large differences in the parameterized convection, and these differences do not cause unexpected behavior in ETC precipitation sensitivity to cyclone moisture or surface wind speed.

Large-scale heavy precipitation over central Europe and the role of atmospheric cyclone track types.

ABSTRACTPrecipitation patterns over Europe are largely controlled by atmospheric cyclones embedded in the general circulation of the mid‐latitudes. This study evaluates the climatologic features of precipitation for selected regions in central Europe with respect to cyclone track types for 1959–2015, focusing on large‐scale heavy precipitation.The analysis suggests that each of the cyclone track types is connected to a specific pattern of the upper level atmospheric flow, usually characterized by a major trough located over Europe. A dominant upper level cut‐off low (COL) is found over Europe for strong continental (CON) and van Bebber's type (Vb) cyclones which move from the east and southeast into central Europe. Strong Vb cyclones revealed the longest residence times, mainly due to circular propagation paths.The central European cyclone precipitation climate can largely be explained by seasonal track‐type frequency and cyclone intensity; however, additional factors are needed to explain a secondary precipitation maximum in early autumn. The occurrence of large precipitation totals for track events is strongly related to the track type and the region, with the highest value of 45% of all Vb cyclones connected to heavy precipitation in summer over the Czech Republic and eastern Austria. In western Germany, Atlantic winter cyclones are most relevant for heavy precipitation. The analysis of the top 50 precipitation events revealed an outstanding heavy precipitation period from 2006 to 2011 in the Czech Republic, but no gradual long‐term change. The findings help better understand spatio‐temporal variability of heavy precipitation in the context of floods and may be used for evaluating climate models.

Location-based environmental factors contributing to rainfall-triggered debris flows in the Ba river catchment, northwest Viti Levu island, Fiji

Mass movements in tropical Pacific small island developing states (SIDS) can be devastating although studies are relatively few and contributing environmental factors are not often investigated in detail. On 25 January 2012, following 3 days of heavy monsoonal rainfall (c. 550 mm) during a La Nina episode, more than 150 debris flows were triggered in the western part of the Ba river catchment of northwest Viti Levu island, Fiji. Reconnaissance field survey and geographical information system (GIS) analyses using high-resolution satellite imagery were carried out to investigate factors that may have led to the occurrence of the debris flows in the catchment. We evaluated the correlation between the density of mass movements (number of mass movements/km2) and several continuous variables using data measured within the GIS. There was a weak but significant positive correlation between mass movement density and elevation (r = 0.38, p value < 0.01), cyclonic precipitation (r = 0.37, p value < 0.01) and stream density (r = 0.31, p value < 0.01). Ninety-three percent of the mass movements occur within a plantation of Pinus caribaea (Caribbean pine) on slopes oriented mainly to the northeast and east on (trade) windward slopes and may be significant factors for their development. Although forests generally have a stabilizing effect on slopes, the plantation at Ba was a mature stand on its second plantation cycle and is a species that has a shallow rooting system making it more susceptible to failure.