Participatory GIS-Based Approach for the Demarcation of Village Boundaries and Their Utility: A Case Study of the Eastern Boundary of Wilpattu National Park, Sri Lanka

This study examines spatial knowledge of the local community and the participatory resource mapping (PRM) approach to demarcate land boundaries in the eastern boundary of Wilpattu National Park, Sri Lanka. Sri Lanka has four types of major administrative boundaries, namely, provinces, districts, divisional secretariat divisions (DSD), and Grama Niladari (GN) divisions. The smallest community segments are clustered inside each GN division. The lack of proper demarcation of these smallest community segments, called ‘villages’, has been identified as a significant issue when implementing community development plans and applications in government and non-government projects. Thus, the deliverables of community-based projects become less effective. The objective of this study was to explore means of demarcating land boundaries, to separately identify small community segments using participatory GIS (PGIS) techniques. The study was conducted covering 12 GN divisions adjoining the eastern border of Wilpattu National Park (WNP). The methods used included PGIS interviews and group discussions with PRM steps. Overall, around 100 selected community members, spread across 12 GN divisions, were chosen to participate in the study. Community society meetings were conducted in each village, and essential topographic information in the area was collected with the knowledge of local society members and GIS tools. Later, this was digitized and verified to improve the presentation and accuracy of the results. As a result, the study could identify villages in each GN division, while generating more precise digital maps. Through this study, it can be confirmed that PGIS has remarkable potential in land use planning applications. The study further shows the potential of the application of PGIS in community-based projects and their deliverables to the community, and in enhancing community education on spatial thinking and planning, while facilitating community empowerment and innovation.

Similarities and Contrasts in Time-Mean Striated Surface Tracers in Pacific Eastern Boundary Upwelling Systems: The Role of Ocean Currents in Their Generation

Eastern boundary upwelling systems feature strong zonal gradients of physical and biological properties between cool, productive coastal oceans and warm, oligotrophic subtropical gyres. Zonal currents and jets (striations) are therefore likely to contribute to the transport of water properties between coastal and open oceanic regions. For the first time, multi-sensor satellite data are used to characterize the time-mean signatures of striations in sea surface temperature (SST), salinity (SSS), and chlorophyll-a (Chl-a) in subtropical eastern North/South Pacific (ENP/ESP) upwelling systems. In the ENP, tracers exhibit striated patterns extending up to ~2500 km offshore. Striated signals in SST and SSS are highly correlated with quasi-zonal jets, suggesting that these jets contribute to SST/SSS mesoscale patterns via zonal advection. Striated Chl-a anomalies are collocated with sea surface height (SSH) bands, a possible result of mesoscale eddy trains trapping nutrients and forming striated signals. In the ESP, the signature of striations is only found in SST and coincides with the SSH bands, consistently with quasi-zonal jets located outside major zonal tracer gradients. An interplay between large-scale SST/SSS advection by the quasi-zonal jets, mesoscale SST/SSS advection by the large-scale meridional flow, and eddy advection may explain the persistent ENP hydrographic signature of striations. These results underline the importance of quasi-zonal jets for surface tracer structuring at the mesoscale.

Role of the eastern boundary-generated waves on the termination of 1997 Indian Ocean Dipole event

The termination of Indian Ocean Dipole (IOD) events is examined in terms of equatorial wave dynamics. In situ and satellite observations combined with an output from a linear wave model are used in this study. Our emphasis is on the 1997 IOD event but our results apply to other positive IOD events as well. We find that the termination of anomalously cold sea surface temperature (SST) in the eastern pole of the dipole is associated with a warming tendency caused by the net surface heat fluxes. However, net surface heat fluxes alone cannot explain the total change in the SST. We show that during the peak phase of an IOD event, the weakening of zonal heat advection caused by eastern boundary-generated Rossby waves combined with the reduction of vertical entrainment and diffusion creates favorable conditions for surface heat fluxes to warm the SST in the eastern basin.

Blue-shifted Deep Ocean Currents in the Equatorial Indian Ocean

Spectra from two decades of zonal current data at ∼ 4000 m in the central and western equatorial Indian Ocean show a shift in the dominant frequencies from the west to the east. The 120–180-day period is stronger at 77ºE , the 60–120-day period at 83ºE, and the 30–90-day period at 93ºE. The weakening of lower frequencies near the eastern boundary can be explained using theoretical ray paths of Kelvin waves and reflected Rossby waves. The equatorial Kelvin wave forced by winds reflects from the eastern boundary as Rossby waves with different meridional modes. After reflection, the low (high) frequency Rossby beams travel a larger (shorter) distance before reaching the bottom, thereby creating a shadow zone, a region with low wave energy, between the ray path and the eastern boundary. The shift in frequency with longitude is not evident in the top 1000 m, where the current is dominated by the semi-annual cycle.