Warm Phase Of El Nino-Southern Oscillation Research Articles

ENSO signatures observed in tropical tropopause layer parameters using long-term COSMIC RO data

The El Nino Southern Oscillation (ENSO) signatures interpreted in different tropical tropopause layer (TTL) parameters are investigated by using long-term Constellation Observing System for Meteorology, Ionosphere, and Climate (COSMIC)-1 radio occultation temperature data from July 2006 to March 2019. The TTL parameters include the cold point tropopause height (CPT-H) and corresponding temperature (CPT-T), lapse rate tropopause height (LRT-H) and corresponding temperature (LRT-T), convective outflow level height (COH), and TTL thickness. Results indicate that the warm phase of ENSO is associated with prominent negative CPT-T anomalies, whereas the cold phase of ENSO is associated with positive CPT-T anomalies over the tropical central and eastern Pacific Ocean. Further, correlation analysis is carried out between TTL parameters obtained over the Nino 3.4 region (5°N–5°S, 170°W–120°W) and sea surface temperature Nino 3.4 Index. We found weak positive correlations in CPT-H (0.37) and LRT-H (0.49), and moderate negative correlations in CPT-T (− 0.62), LRT-T (− 0.64), and TTL thickness (− 0.5) with Nino 3.4 Index. Interestingly, a higher correlation of 0.8 is noticed between COH and the Nino 3.4 Index. Furthermore, lag correlation analysis reveals that a 4-month lag is noticed in tropopause heights (CPT-H and LRT-H) and a 2-month lag is evident in tropopause temperatures (CPT-T and LRT-T) with the Nino 3.4 Index. In addition, only 1-month lag is noticed between COH and Nino 3.4 index. With a high correlation and 1-month lag with the Nino 3.4 index, it is concluded that the COH is the most suitable TTL parameter to detect the ENSO signatures among the TTL parameters.

Effect of winter-to-summer El Niño transitions on tropical cyclone activity in the North Atlantic

El Nino-Southern Oscillation (ENSO) is known to significantly modulate Atlantic tropical cyclone (TC) activity. In this paper, we separate El Nino events into El Nino resurgence (ELR) and La Nina-transition-El Nino (LAT) events according to the warm or cold ENSO phase in the preceding winter. Different influences of the two types of El Nino events on North Atlantic TC activity are explored during the hurricane season of June–November. The average number of TCs is more, with shorter average duration and slightly larger intensity during ELR events than during LAT events. There are more TCs passing through and making landfall at the Gulf of Mexico, Caribbean Sea during ELR events, indicating that TCs may have a greater impact on coastal cities of Gulf of Mexico and Caribbean Sea during ELR events than LAT events. Composite analysis reveals that thermodynamic factors such as relative humidity (RH), sea surface temperature and tropical cyclone heat potential are mainly responsible for the TC activity difference between ELR and LAT events. Genesis potential index diagnosis shows that the RH and potential intensity are the dominant factors that influence TC genesis in the MDR during ELR events. During LAT events, the relative vorticity, vertical wind shear and RH over Cape Verde are favorable for TC genesis. In summary, the preceding winter ENSO phases associated with ELR and LAT events lead to opposite changes of environmental factors, and thus induce different TC activities in ELR and LAT events.

ENSO influence on summer temperature over Arabian Peninsula: role of mid-latitude circulation

This study discusses the interannual variability of the summer (June–August) season surface air temperature (SAT) over the Arabian Peninsula and its relationship to the global circulation patterns under the influence of El Nino Southern Oscillation (ENSO). A composite analysis based on the above (below) normal summer SAT over the Arabian Peninsula reveals a wavelike pattern resembling the mid-latitude Circumglobal Wave Train (CGT). The positive (negative) phase of the CGT is associated with above (below) normal SAT anomalies over the Arabian Peninsula. Further, the Arabian Peninsula summer SAT is also found to be associated with ENSO and this association has strengthened in recent decades as compared to before 1980s. The ENSO induced upper level circulation patterns resemble the CGT pattern. The ENSO warm phase over the central and eastern Pacific is associated with anomalous low pressure anomalies over the Eurasian region while the cold phase associated with anomalous high pressure. This favours the above normal SAT anomalies over the Eurasian region including the northern parts of the Peninsula during the cold phase of ENSO and below normal temperature during the warm phase. The weakening of upper level low-pressure anomalies over central Asia during the positive phase of CGT also favours the extension of the Eurasian high over the Arabian Peninsula. Additionally, the climate model simulations experiments performed with newly developed Saudi-KAU Atmospheric Global Climate Model (AGCM) also support the observed findings.

Investigating the Teleconnection between Warm ENSO Phases and Seasonal Rainfall over Kotmale Catchment in Sri Lanka

Seasonal rainfall over Kotmale reservoir is changing at an alarming rate due to atmospheric oscillations taking place over Sri Lanka. Therefore, this study focused on the teleconnection between warm El-Nino Southern Oscillation (ENSO) phases and rainfall over the Kotmale catchment. Daily rainfall data obtained from 11 meteorological stations were used to identify the behaviour of the annual rainfall climatologies of the catchment. Inflow data of the Kotmale reservoir obtained for the period 1984 to 2012 were analysed to understand reservoir inflow trends. Sea surface temperatures were obtained from Japan Meteorological Agency to determine the warm El- Nino Southern Oscillation phase. The rainfall at the stations and the inflow to the reservoir have declined over the period selected. However, the rate of decrease has varied from station to station. Seasonal rainfall at all the stations considered between December and September showed a negative correlation with the mean sea surface temperature of the Nino 3 region. Warm El-Nino Southern Oscillation caused below average seasonal rainfall over the catchment between December and September. The northeast and southwest monsoon rainfall over the catchment has weakened because of warm El-Nino Southern Oscillation phase in the Nino 3 region. However, the effect has got reduced with the onset of monsoons.

Assessment of the Teleconnection Between El Nino Southern Oscillation (ENSO) and West African Rainfall

In this study, rainfall variability over Nigeria was analysed in relation to ocean-atmospheric interaction due to ENSO event. Monthly rainfall data were collected from Nigerian Meteorological Agency (NIMET) from six (6) synoptic stations selected across three (3) geographical regions in Nigeria for a period of 26 years (1988 - 2013). Cluster analysis grouped the rainfall data into three clusters namely Coastal South, Middle belt and Sahel North, while Southern Oscillation Index (SOI) data from 1988 to 2013 was retrieved from National Ocean Atmospheric Administration (NOAA) as updated by the National Centre for Environmental Prediction (NCEP). Rainfall Analysis Index (RAI) was computed for each of the three sub-regions and respective anomalies revealed in a time series. Additionally, linear correlation analysis between the RAI and SOI were computed at lag three months to determine any relationship between ENSO and Nigerian rainfall. The result shows that correlation between RAI and SOI were not uniformly significant, with Region 1 having a positive correlation and a negative correlation recorded for regions 2 and 3. Likewise, simple matrix confirm for region 1 the positive rainfall anomalies occurring during warm ENSO phase. How forecast will be improved if ENSO indices are included as precursor variables in rainfall forecast for the region will be of interest.Key Words: El Nino Southern Oscillation, Nigerian rainfall, Southern Oscillation Index (SOI)

Monitoring Water Resources over the Kotmale Reservoir in Sri Lanka Using ENSO Phases

In this study, the El Nino Southern Oscillation (ENSO) phase index is used for water management over the Kotmale reservoir in Sri Lanka. Daily rainfall data of 9 stations over the Kotmale catchment during 1960–2005 June-September (JJAS) season is investigated over the Kotmale catchment. The ENSO phases are identified based on the 0.5°C sea surface temperature (SST) anomaly over Nino 3 region. The study has brought out few stations showing increasing and a few decreasing seasonal rainfall trends for JJAS season, while there is no change in the annual rainfall for the catchment. Monthly and seasonal rainfall of all the selected stations showed negative correlation with the sea surface temperature (SST) over the Nino-3 region index during JJAS season with varying magnitudes. During the warm phase of ENSO, below average rainfall is prominent for JJAS season over many stations. The rainfall especially during early September showed a significant below average rainfall during the warm ENSO phase. The seasonal rainfall during neutral and cold ENSO phases does not experience similar significant changes as seen during warm ENSO phase. Inflow of the Kotmale reservoir shows decreasing trend for the period of 1960–2005 in the observation from all stations collectively.

Decadal modulation of East China winter precipitation by ENSO

The decadal modulation of East China winter precipitation by the El Nino-Southern Oscillation (ENSO) is examined using both observational data and coupled global climate model simulations. The co-variability between 68-year (1948–2015) observed East China precipitation and tropical Pacific sea surface temperature (SST) is quantified by the singular value decomposition (SVD) method. The first SVD mode relates Southeast China winter pluvial (drought) to the tropical Pacific El Nino (La Nina) SST. A comparison between two 480-year model simulations with and without ENSO suggests that ENSO can modulate both the intensity and frequency of East China winter precipitation. In the presence of ENSO, maximum precipitation anomalies over Southeast China can be increased by 50% and largely on the interannual timescale (3–6 years). It is also demonstrated that there is an asymmetry in the precipitation and circulation responses to warm and cold phases of ENSO. The responses are sensitive to the intensity of SST anomalies during El Nino, but less sensitive to SSTs during La Nina. This sensitivity, together with the decadal variations of ENSO, helps understand the observed decadal changes in the strength of the association between wintertime tropical Pacific SST and East China precipitation. The association is relatively weak during 1948–1977 when La Nina occurred more frequently, but strong during 1978–1999 when El Nino occurred more frequently. In the last 16 years (2000–2015) the association is weakest, likely due to the weakened variability of tropical Pacific SST since 2000.

ENSO related SST anomalies and relation with surface heat fluxes over south Pacific and Atlantic

The role of surface heat fluxes in Southern Pacific and Atlantic Ocean SST anomalies associated with El Nino Southern Oscillation (ENSO) is studied using observation and ocean reanalysis products. A prominent dipole structure in SST anomaly is found with a positive (negative) anomaly center over south Pacific (65S–45S, 120W–70W) and negative (positive) one over south Atlantic (50S–30S, 30W–0E) during austral summer (DJF) of El Nino (LaNina). During late austral spring-early summer (OND) of El Nino (LaNina), anomalous northerly (southerly) meridional moisture transport and a positive (negative) sea level pressure anomaly induces a suppressed (enhanced) latent heat flux from the ocean surface over south Pacific. This in turn results in a shallower than normal mixed layer depth which further helps in development of the SST anomaly. Mixed layer thins further due to anomalous shortwave radiation during summer and a well developed SST anomaly evolves. The south Atlantic pole exhibits exactly opposite characteristics at the same time. The contribution from the surface heat fluxes to mixed layer temperature change is found to be dominant over the advective processes over both the basins. Net surface heat fluxes anomaly is also found to be maximum during late austral spring-early summer period, with latent heat flux having a major contribution to it. The anomalous latent heat fluxes between atmosphere and ocean surface play important role in the growth of observed summertime SST anomaly. Sea-surface height also shows similar out-of-phase signatures over the two basins and are well correlated with the ENSO related SST anomalies. It is also observed that the magnitude of ENSO related anomalies over the southern ocean are weaker in LaNina years than in El Nino years, suggesting an intensified tropics-high latitude tele-connection during warm phases of ENSO.

Variability of the Caribbean low-level jet during boreal winter: large-scale forcings

An index capturing the anomalies of the zonal wind at 925 hPa from 1950 to 2010 was defined to explore the relationship between the fluctuations of the Caribbean low-level jet (CLLJ) and the main climate variability modes affecting the Intra-Americas Sea Region. El Nino Southern Oscillation (ENSO) events, here defined using the Nino 3.4 index, are found to be the most important variability modes for the jet anomalies, in agreement with previous studies. However, the Pacific Decadal Oscillation (PDO) and the Pacific/North American (PNA) teleconnection pattern also show significant correlations with the CLLJ anomaly index during February. The North Atlantic Oscillation (NAO) and the Arctic Oscillation (AO) reveal a possible interaction with the jet anomalies that could be connected with the cold fronts and cold air surges arriving to the Caribbean basin from the Northern Hemisphere during winter. A composite technique is used to explain the correlations with the Pacific indexes. We found that ENSO events are connected to CLLJ anomalies by modulating the sea-level pressure (SLP) near the east coast of the United States and the Aleutian Low. The pattern displayed by the SLP anomalies (SLPa) is also associated with the PNA. During warm (cold) ENSO phases, negative (positive) anomalies in the SLP field over the east coast of North America produce cyclonic (anticyclonic) circulations at low levels. However, the ENSO signal in the SLPa and the PNA pattern are modulated by the phases of the PDO. Results indicate that when the ENSO and PDO are in phase (out of phase), the SLPa signal is enhanced (weakened or cancelled), affecting the CLLJ anomalies in both direction and intensity, also changing the spatial distribution of precipitation.

Climate regimes, El Niño-Southern oscillation and konzo epidemics

Epidemics of konzo have occurred during severe droughts in parts of east, central, and southern Africa since the 1920s. Occurrence is attributed to exposure to cyanide from poorly processed cassava foods, the sole source of calories when other food crops fail. El Nino, the warm phase of the El Nino-Southern Oscillation (ENSO), induces severe droughts in the geographical areas of Africa where epidemics of konzo occur. Climate regimes are determined by modes of Pacific Decadal Oscillation, which modulates the ENSO. Study was done to determine the relationship of konzo epidemics to climate regimes and phases of ENSO, and to propose a model to explain while konzo epidemics do not occur in all drought affected areas. Data of all konzo epidemics in the past century and in DR Congo from 1974–1996, and indices of ENSO and PDO from 1915 to 2014 were obtained. Konzo epidemics were mapped to phases of ENSO and PDO. Wavelet spectral and wavelet spectral coherence analysis of climate indices and konzo epidemics were done. All konzo epidemics of the past century occurred during warm climate regimes. Of 19 warm phases of ENSO from 1974–1996 in DR Congo, 17 were coupled to konzo epidemics, while of 4 cold phases of ENSO, 1 was coupled to konzo epidemic, odds ratio 26 (95 % CI, 2–378). Global spectral of ENSO and konzo showed dominant periodicity of 5 years, while spectograms showed significant periodicities and coherence between 3–6 years. Spatial distribution of konzo is restricted to the area of maximal impact of El Nino on precipitation in Africa. El Nino is the underlying cause of konzo epidemics. Control of konzo epidemics requires management of the impact of El Nino on agriculture in areas where the population depends on cassava as sole source of calories during droughts. There is the need to develop forecast models of changes in cassava production to predict likely periods of konzo epidemics.

El Niño-southern oscillation and cassava production in Tanzania and Brazil

Konzo epidemics occur during droughts in East, Central, and Southern Africa, where the population depends almost exclusively on poorly processed cassava. Warm phases of El Nino-Southern Oscillation (ENSO) and Pacific decadal Oscillation (PDO) are associated with droughts in these areas of Africa, but with increase rainfall in South America. To further understanding of the relationship of droughts, cassava production, and konzo epidemics, this study was done to determine if there is coherence of spectra of ENSO, PDO and cassava production. Annual time series of cassava production in Tanzania and Brazil, multivariate ENSO index (MEI), and the Pacific Decadal Oscillation index (PDO) from 1961–2013 were compared. Wavelet and cross wavelet analyses of cassava production, ENSO, and PDO were performed. Warm phases of ENSO and PDO were associated with high cassava production in Tanzania, but with low cassava production in Brazil. Spectrogram of cassava showed significantly high production at periodicities of 3–9 years in Tanzania, but with significantly low production at periodicities of 2–6 years in Brazil. Cross wavelet spectrograms showed coherence of cassava production, ENSO and PDO in Tanzania and Brazil. Time-varying cyclical cassava production in Tanzania and Brazil are coupled to ENSO and PDO modes. Occurrence of droughts, high cassava production, and konzo epidemics in Tanzania are attributable to the impact of climate variability, which should be the focus of public health policies to control konzo epidemics.

The anomalous winter of 1783-1784: Was the Laki eruption or an analog of the 2009-2010 winter to blame?

The multi ]stage eruption of the Icelandic volcano Laki beginning in June, 1783 is speculated to have caused unusual dry fog and heat in western Europe and cold in North America during the 1783 summer, and record cold and snow the subsequent winter across the circum-North Atlantic. Despite the many indisputable impacts of the Laki eruption, however, its effect on climate, particularly during the 1783.1784 winter, may be the most poorly constrained. Here we test an alternative explanation for the unusual conditions during this time: that they were caused primarily by a combined negative phase of the North Atlantic Oscillation (NAO) and an El Nino ]Southern Oscillation (ENSO) warm event. A similar combination of NAO ]ENSO phases was identified as the cause of record cold and snowy conditions during the 2009.2010 winter in Europe and eastern North America. 600-year tree-ring reconstructions of NAO and ENSO indices reveal values in the 1783.1784 winter second only to their combined severity in 2009.2010. Data sources and model simulations support our hypothesis that a combined, negative NAO ]ENSO warm phase was the dominant cause of the anomalous winter of 1783.1784, and that these events likely resulted from natural variability unconnected to Laki.

Early Larval Development ofDonax obesulus:Response to el Niño Temperature and Salinity Conditions

The Humboldt Current System is a highly productive ecosystem that is subject to the dynamics of the El Nino Southern Oscillation (ENSO). El Nino (EN, the warm phase of ENSO) causes vital changes in surface water temperature, oxygen levels, and salinity conditions, which arc reflected in various responses of coastal pelagic and benthic organisms. For very shallow habitats such as sandy beaches, temperature and salinity are considered the principal parameters changing during strong EN. However, the mechanisms by which these changes effect change on the structure of coastal populations remains largely unknown. The surf clam Donax ohesulus is dominant on large sandy beaches of the Humboldt Current System. Its biogeographical distribution is largely influenced by EN-induced environmental changes. Despite the species' key role in the beach ecosystem, the effects of modified abiotic conditions on the meroplanktonic larval stages and threshold temperatures involved have not yet been investigated. After EN episodes, meroplanktonic larval stages play a crucial role in the medium- and long-term stability of shallow-water species. Thus, this study makes a first attempt to describe the ontogeny of D. ohesulus and examines the effects on development of EN temperature conditions (ENTC) in comparison with normal temperature conditions (NTC). Results indicate that early life history follows a pattern previously described for other donacid bivalves. Development, growth, and mortality of larvae were assessed during a 3-wk in vitro experiment, indicating that larvae reared under ENTC grew and developed faster in comparison with those reared under NTC; mortality was slightly higher under ENTC. During a 2nd experiment, larvae were exposed for 48 h to a distinct range of different salinities (35, 25, 15, and 5 ± 1) at 2 different temperatures (NTC and ENTC). At both temperatures, larvae suffered no mortality at medium and low salinity (35, 25, and 15 ± 1) but showed 100% mortality at very low salinity (5 ± 1) after 16 h at NTC and 32 h at ENTC. Activity of larvae was highest at medium salinity (25 ± 1) and lowest at normal salinity (35 ± 1). The results of this study indicate that early larval stages of D. ohesulus can cope with temperature and salinity changes induced during EN. Only extremely low salinity (5 ± 1) such as that observed close to river mouths may cause high mortality rates in D. ohesulus offspring.

Changing dependence of Zimbabwean rainfall variability on ENSO and the Indian Ocean dipole/zonal mode

A novel approach of using variability as a major descriptive parameter for observational time series is adopted to investigate how southeastern African (Zimbabwe) summer rainfall may have been forced by the El Nino southern oscillation (ENSO) and/or the Indian Ocean dipole/zonal mode (IODZM), concurrently with the changing sea surface temperature (SST) background of the Indo-Pacific region. The period is from 1901 to 2007. Wavelet power spectrum and linear statistical analysis, including simple and partial correlation techniques, are utilized to achieve this end. The results reveal epochal changes in teleconnections and other statistical properties linking southeastern African rainfall variability to the Indo-Pacific SSTs. These epochs conspicuously exhibit the period around 1945/1946, 1960/1961, 1972/1973, and 1997/1998 as demarcating distinct systematic climate turning points during the century. The role of the 1976/1977 climate regime shift seems not to be that apparent but instead, 1960/1961 and 1997/1998 appear to be the major turning points, both in the teleconnections and Indo-Pacific SST temporal characteristics. From the early 1960s to 1997, as much as 28% of the rainfall variability was linearly related to the IODZM while the ENSO hardly explained a quarter of this value. During this period, droughts are especially strongly connected to the positive IODZM events but insignificantly linked to El Nino, thus contradicting the conventional knowledge attributing most of regional rainfall suppression to the warm ENSO phase. However, the post 1997 epoch saw the reversal of the two climate modes’ influences. ENSO influence evidently became activated, attaining the previously assumed dominant role which had proved elusive during the earlier epochs. But this increased ENSO control is attributed to only less than 12% of the rainfall variance while IODZM seem to be largely decoupled from the local rainfall influencing processes by hardly explaining a drastically reduced 1% of the rainfall variance. This transformation occurred despite of neither ENSO nor IODZM SST anomalies showing any statistically significant changes. As far as could be established, this epochal behavior may not be forced by the frequency and magnitude of ENSO and IODZM events but most probably by the slow processes inherent in the SST background, especially of the tropical Indian Ocean. Thus, the apparent simultaneous decoupling of the IODZM and coupling of the ENSO to the regional rainfall controlling mechanisms seems to be the result of the unprecedented warming of the intervening tropical western Indian Ocean SSTs in the last decade. Consequently, the knowledge of the states of epochal Indian Ocean SST background variability should be an important regional scientific issue, since these epochal variations may dictate the nature (and successful prediction) of interannual as well as decadal climate fluctuations over southeastern Africa.

Regional climate model simulation of winter climate over Central–Southwest Asia, with emphasis on NAO and ENSO effects

AbstractWe present a regional climate modeling study of the winter climate of Central–Southwest Asia (CSWA), focusing on the mean model climatology of temperature and precipitation, the simulated storm characteristics and the effects of El‐Nino Southern Oscillation (ENSO) and North Atlantic Oscillation (NAO) on storm activity and precipitation. Forty‐three winter seasons are simulated with the model RegCM3 driven by ERA40 reanalysis fields over a region encompassing CSWA and the Mediterranean sector. The model shows a good performance in reproducing the observed mean surface climate of the region as well as the characteristics of the western disturbances affecting CSWA. Observations show that both the NAO and ENSO have a substantial influence on the CSWA climate, particularly in the region of Northern Pakistan, Afghanistan and Tajikistan, where precipitation increases (decreases) during the positive (negative) NAO phase and warm (cold) ENSO phase. The model captures well the observed signals and a detailed storm analysis shows that they are mostly associated with an intensification of western disturbances originating in the Eastern Mediterranean and Middle East regions and moving eastward across a 500 hPa trough situated over the CSWA during the positive NAO and warm ENSO phases. The NAO and ENSO signals are reinforced by enhanced moisture sources from the Mediterranean, Caspian and Arabian Seas. Our study provides encouraging indications towards the use of the model RegCM3 for climate simulations over CSWA. Copyright © 2009 Royal Meteorological Society

Spatial and Temporal Variations in Rainfall and the ENSO-rainfall Relationship over Sarawak, Malaysian Borneo

To determine the spatial and temporal variations in the El Nino Southern Oscillation (ENSO)-rainfall relationship and seasonal variation in rainfall over northern Borneo, simultaneous and lag correlations between the December-February (DJF) average Nino-3.4 (5°S-5°N, 170°-120°W) sea surface temperature (SST) and rainfall were examined using rainfall data from 18 stations throughout Sarawak during 1963-2003. The lag correlations for June-August (JJA) rainfall and SST were significantly negative over southwestern Sarawak (SWS), but the simultaneous correlations for DJF rainfall and SST were significantly negative over northeastern Sarawak (NES). We categorized the 18 stations into four clusters (C1-C4) according to the variation of the seasonal fluctuation in rainfall. C1 and C2 are located in SWS along the convex and concave coastline, respectively, whereas C3 and C4 are located in NES along the convex and straight coastline, respectively. C2 and C4 are also located in the interior in SWS and NES respectively. From the composite of monthly rainfall for all clusters, a decrease in rainfall in JJA was found for all regions in El Nino years but only for C2, C3 and C4 in DJF during the warm phase of ENSO. The C3 region may be the most vulnerable to El Nino-induced droughts in Sarawak.

Spatial Ecology of Small Mammals in North-central Chile: Role of Precipitation and Refuges

Lower-elevation habitats of north-central Chile are characterized by semiarid vegetation that is strongly influenced by rainfall related to El Nino Southern Oscillation (ENSO) events. During the ENSO warm phase (i.e., El Nino), heavy rains occur resulting in small mammal irruptions or ratadas. During prevailing drier periods, pronounced droughts result in reductions in small mammal densities and local extinctions of some species. Within the dominant thorn-scrub habitat of a national park, we identified 2 other habitat types, aguadas (riverine shrublands) and fog-forest patches that serve as refuges for small mammals during dry years. We divide small mammal species of the thorn scrub into 2 groups: core species (Octodon degus, Phyllotis darwini, Abrothrix olivaceus, and Thylamys elegans) maintain populations at all times, whereas opportunistic species (Oligoryzomys longicaudatus and A. longipilis) are present only after rains. The latter group appears to maintain refuge populations in aguadas and fog forests and to opportunistically exploit the thorn scrub when conditions are favorable. Aguadas also may play an important role in the persistence of less-common species, such as Octodon lunatus and Abrocoma bennetti. Despite being small and patchily distributed, aguadas are important for the maintenance of regional biodiversity.

Grazing effects of the periwinkle Echinolittorina peruviana at a central Peruvian high rocky intertidal

Echinolittorina peruviana is the most common gastropod in the high intertidal zone of Peru, representing more than 80% of the individuals present at that zone. Experimental removal of snails was used to evaluate their effects on (a) abundance of epilithic biofilm, (b) barnacle recruitment, and (c) abundance of macroalgae under “normal” conditions of the El Nino Southern Oscillation (ENSO). Experiments were carried out from October 2005 to April 2007 at two intertidal levels of a semi-protected rocky shore of central Peru. Results demonstrated that E. peruviana is able to control biofilm abundance and barnacle recruitment at both heights investigated, with marked effects in the lower zone. Erect macroalgae (Ulva spp. and Gelidium spp.) were less affected by grazing; but negative effects were observed on macroalgal crusts. Season and physical stress seem to play a more important role in the abundance of macroalgae in the high intertidal. Our results are similar to those reported elsewhere for high shore littorinids and represent baseline data to understand how the role of intertidal consumers will vary under the cold (La Nina) and warm (El Nino) phases of ENSO on these shores.

Predictability of stream flow and rainfall based on ENSO for water resources management in Sri Lanka

Summary We investigate the viability of using El Nino-Southern Oscillation (ENSO) and sea surface temperature (SST) data to predict seasonal streamflow for one of the major rivers in Sri Lanka, the Kelani, using correlation analysis, contingency tables, and principal component analysis. The agricultural seasons in Sri Lanka are Yala (April-September) and Maha (October-March). The correlation between the Kelani River streamflow during Yala and ENSO indices (r = � 0.41) is significant at 99% level. In addition, the Kelani streamflow during Yala has a correlation with the Central Indian Ocean SST (r = � 0.40) that is also sig- nificant at the 99% level. The first principal component of the Indo-Pacific Ocean SST is reminiscent of the SST associated with the ENSO mode. A prediction scheme based on this mode for the streamflow during Yala has a skill characterized by a correlation of 0.5 in a cross-validated mode. The prediction of streamflow during Maha is best carried out separately for the two halves of the season. During the El Nino phase, the rainfall during Maha is enhanced during the first half of the season (October-December) and diminished in the second half (Jan- uary-February). Rainfall rather than streamflow has a better relationship with ENSO from October to December. During the second half of the Maha season, rainfall declines with both warm and cold ENSO phases and any prediction scheme has to take into account this non-linear relationship. Overall, useful skill for seasonal streamflow predictions has been demonstrated for the Yala season and skill for seasonal rainfall predictions for the first and second half of the Maha season has been elucidated. a 2006 Elsevier B.V. All rights reserved.

The response of precipitation and surface hydrology to tropical macro‐climate forcing in Colombia

AbstractIn tropical South America, weather and climate are affected by the meridional oscillation of the inter‐tropical convergence zone, the Pacific and Atlantic oceans, the Amazon basin, and the Andes Mountains. The dominant mode of the inter‐annual climate variability in the tropical Pacific is the El Niño/Southern Oscillation (ENSO) phenomenon. Colombia is among the South American countries that experiences large climate anomalies because of ENSO. However, the hydrologic response in Colombia to a particular ENSO event is highly complex and non‐linear.To describe this complex, non‐linear hydro‐climatic response to large‐scale atmospheric forcing in Colombia, a one‐way coupled atmospheric‐land surface hydrologic modelling approach is implemented whose main components are Colorado State University's Regional Atmospheric Modelling System (RAMS) and the Swedish Hydrologiska Byråns Vattenbalansavdelning‐Hydrologic Modelling System (HBV‐HMS). RAMS is implemented in a two‐nested grid domain for seasonal simulations and a four‐nested grid domain for daily simulations. Seasonal simulations emphasize the annual cycle at regional scales, while daily simulations focus on describing the diurnal cycle for specific watersheds. The HBV‐HMS is implemented for a specific watershed and used to examine its response at daily time scales.Results of the seasonal simulations reproduce quite well the observed spatial and temporal patterns of the hydro‐climatic variables: simulated temperature, pressure, wind velocity, and precipitation distributions show good agreement with observations. Results also show that the 1992 warm phase of ENSO led to a generalized decrease of precipitation along the Andes ranges and that the low lands of Colombia received more precipitation than during the 1989 cold ENSO phase. Similarly, daily‐simulated fields show good agreement with observed values. However, the simulated diurnal cycle of precipitation exhibits a temporal phase lag of several hours and simulated precipitation tends to underestimate both the total amount of precipitation and the duration of precipitation events. Despite these discrepancies, the results of the modelling effort clearly demonstrate the ability of this approach to capture the non‐linear and complex interactions of large‐scale atmospheric forcing and local characteristics as indicated by the satisfactory simulation of stream flow responses for a set of small watersheds. Copyright © 2006 John Wiley & Sons, Ltd.